----

----

|   | x | QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 |
|--------|---|---------------------------------------------------------------------------------------------------|

|   | o | TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 |
|--------|---|----------------------------------------------------------------------------------------------------|

| Colorado                                                       |   | 84-0296600                           |
|----------------------------------------------------------------|--------|--------------------------------------|
| (State or other jurisdiction of incorporation or organization) |   | (I.R.S. Employer Identification No.) |
|                                                           |   |                                 |
| 1800 Larimer, Suite 1100                                       |   |                                 |
| Denver, Colorado                                               |   | 80202                                |
| (Address of principal executive offices)                       |   | (Zip Code)                           |

| Large accelerated filer o                   |   | Accelerated filer o         |
|---------------------------------------------|--------|-----------------------------|
|                                        |   |                        |
| Non-accelerated filer x                     |   | Smaller reporting company o |
| (Do not check if smaller reporting company) |   |                        |

| Class                         |   | Outstanding at May 2, 2011 |
|-------------------------------|--------|----------------------------|
| Common Stock, $0.01 par value |   | 100 shares                 |

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TABLE OF CONTENTS

| PART I - FINANCIAL INFORMATION      |                                                                                        |
|------------------------------------------|---------------------------------------------------------------------------------------------|
|                                     |                                                                                        |   |
| Item l.                                  | Financial Statements (Unaudited)                                                            | 3 |
| Item 2.                                  | Management’s Discussion and Analysis of Financial Condition and Results of Operations | 22 |
| Item 4.                                  | Controls and Procedures                                                                     | 27 |
|                                     |                                                                                        |   |
| PART II - OTHER INFORMATION         |                                                                                        |
|                                     |                                                                                        |   |
| Item 1.                                  | Legal Proceedings                                                                           | 27 |
| Item 1A.                                 | Risk Factors                                                                                | 27 |
| Item 6.                                  | Exhibits                                                                                    | 27 |
|                                     |                                                                                        |   |
| SIGNATURES                               | 28                                                                                          |
|                                     |
| Certifications Pursuant to Section 302   | 1                                                                                           |
| Certifications Pursuant to Section 906   | 1                                                                                           |
| Statement Pursuant to Private Litigation | 1                                                                                           |

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Table of Contents

Item 

|                                                                                       |   | Three Months Ended March 31, |      |
|--------------------------------------------------------------------------------------------|--------|------------------------------|-----------|
|                                                                                       |   | 2011                         |      |   | 2010 |   |
| Operating revenues                                                                         |   |                         |      |   |   |   |
| Electric                                                                                   |   | $                            | 704,153   |   |   | $ | 723,634 |   |
| Natural gas                                                                                |   |                         | 428,191   |   |   |   | 466,283 |   |
| Steam and other                                                                            |   |                         | 12,103    |   |   |   | 12,780 |   |
| Total operating revenues                                                                   |   |                         | 1,144,447 |   |   |   | 1,202,697 |   |
|                                                                                       |   |                         |      |   |   |   |   |   |
| Operating expenses                                                                         |   |                         |      |   |   |   |   |   |
| Electric fuel and purchased power                                                          |   |                         | 323,797   |   |   |   | 373,851 |   |
| Cost of natural gas sold and transported                                                   |   |                         | 304,938   |   |   |   | 340,709 |   |
| Cost of sales — steam and other                                                      |   |                         | 5,121     |   |   |   | 6,073 |   |
| Other operating and maintenance expenses                                                   |   |                         | 170,671   |   |   |   | 155,693 |   |
| Demand side management program expenses                                                    |   |                         | 30,322    |   |   |   | 33,711 |   |
| Depreciation and amortization                                                              |   |                         | 79,969    |   |   |   | 66,966 |   |
| Taxes (other than income taxes)                                                            |   |                         | 34,321    |   |   |   | 24,616 |   |
| Total operating expenses                                                                   |   |                         | 949,139   |   |   |   | 1,001,619 |   |
|                                                                                       |   |                         |      |   |   |   |   |   |
| Operating income                                                                           |   |                         | 195,308   |   |   |   | 201,078 |   |
|                                                                                       |   |                         |      |   |   |   |   |   |
| Other income, net                                                                          |   |                         | 1,663     |   |   |   | 556 |   |
| Allowance for funds used during construction —  equity                     |   |                         | 1,619     |   |   |   | 2,978 |   |
|                                                                                       |   |                         |      |   |   |   |   |   |
| Interest charges and financing costs                                                       |   |                         |      |   |   |   |   |   |
| Interest charges — includes other financing costs of $1,516 and $1,397, respectively |   |                         | 45,399    |   |   |   | 45,813 |   |
| Allowance for funds used during construction — debt                                  |   |                         | (726      | ) |   |   | (1,665 | ) |
| Total interest charges and financing costs                                                 |   |                         | 44,673    |   |   |   | 44,148 |   |
|                                                                                       |   |                         |      |   |   |   |   |   |
| Income before income taxes                                                                 |   |                         | 153,917   |   |   |   | 160,464 |   |
| Income taxes                                                                               |   |                         | 57,287    |   |   |   | 76,214 |   |
| Net income                                                                                 |   | $                            | 96,630    |   |   | $ | 84,250 |   |

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Table of Contents

|                                                                          |   | Three Months Ended March 31, |     |
|-------------------------------------------------------------------------------|--------|------------------------------|----------|
|                                                                          |   | 2011                         |     |   | 2010 |   |
| Operating activities                                                          |   |                         |     |   |   |   |
| Net income                                                                    |   | $                            | 96,630   |   |   | $ | 84,250 |   |
| Adjustments to reconcile net income to cash provided by operating activities: |   |                         |     |   |   |   |   |   |
| Depreciation and amortization                                                 |   |                         | 81,284   |   |   |   | 68,163 |   |
| Demand side management program amortization                                   |   |                         | 2,546    |   |   |   | 7,281 |   |
| Deferred income taxes                                                         |   |                         | 47,172   |   |   |   | 36,989 |   |
| Amortization of investment tax credits                                        |   |                         | (668     | ) |   |   | (584 | ) |
| Allowance for equity funds used during construction                           |   |                         | (1,619   | ) |   |   | (2,978 | ) |
| Net realized and unrealized hedging and derivative transactions               |   |                         | 18,520   |   |   |   | (10,048 | ) |
| Changes in operating assets and liabilities:                                  |   |                         |     |   |   |   |   |   |
| Accounts receivable                                                           |   |                         | 11,885   |   |   |   | 5,822 |   |
| Accrued unbilled revenues                                                     |   |                         | 76,879   |   |   |   | 100,139 |   |
| Inventories                                                                   |   |                         | 37,815   |   |   |   | 51,746 |   |
| Prepayments and other                                                         |   |                         | 28,913   |   |   |   | 43,613 |   |
| Accounts payable                                                              |   |                         | (55,823  | ) |   |   | (120,659 | ) |
| Net regulatory assets and liabilities                                         |   |                         | 2,239    |   |   |   | (16,279 | ) |
| Other current liabilities                                                     |   |                         | 43,374   |   |   |   | 55,578 |   |
| Pension and other employee benefit obligations                                |   |                         | (57,910  | ) |   |   | (4,349 | ) |
| Change in other noncurrent assets                                             |   |                         | (283     | ) |   |   | (1,489 | ) |
| Change in other noncurrent liabilities                                        |   |                         | (5,588   | ) |   |   | (7,773 | ) |
| Net cash provided by operating activities                                     |   |                         | 325,366  |   |   |   | 289,422 |   |
|                                                                          |   |                         |     |   |   |   |   |   |
| Investing activities                                                          |   |                         |     |   |   |   |   |   |
| Utility capital/construction expenditures                                     |   |                         | (115,991 | ) |   |   | (115,890 | ) |
| Allowance for equity funds used during construction                           |   |                         | 1,619    |   |   |   | 2,978 |   |
| Net cash used in investing activities                                         |   |                         | (114,372 | ) |   |   | (112,912 | ) |
|                                                                          |   |                         |     |   |   |   |   |   |
| Financing activities                                                          |   |                         |     |   |   |   |   |   |
| Repayment of short-term borrowings, net                                       |   |                         | (227,400 | ) |   |   | (59,000 | ) |
| Borrowings under utility money pool arrangement                               |   |                         | 120,000  |   |   |   | 147,900 |   |
| Repayments under utility money pool arrangement                               |   |                         | (120,000 | ) |   |   | (224,900 | ) |
| Capital contributions from parent                                             |   |                         | 75,000   |   |   |   | - |   |
| Dividends paid to parent                                                      |   |                         | (66,828  | ) |   |   | (65,822 | ) |
| Net cash used in financing activities                                         |   |                         | (219,228 | ) |   |   | (201,822 | ) |
|                                                                          |   |                         |     |   |   |   |   |   |
| Net decrease in cash and cash equivalents                                     |   |                         | (8,234   | ) |   |   | (25,312 | ) |
| Cash and cash equivalents at beginning of period                              |   |                         | 32,912   |   |   |   | 33,429 |   |
| Cash and cash equivalents at end of period                                    |   | $                            | 24,678   |   |   | $ | 8,117 |   |
|                                                                          |   |                         |     |   |   |   |   |   |
| Supplemental disclosure of cash flow information:                             |   |                         |     |   |   |   |   |   |
| Cash paid for interest (net of amounts capitalized)                           |   | $                            | (39,145  | ) |   | $ | (34,225 | ) |
| Cash received for income taxes, net                                           |   |                         | 33,696   |   |   |   | 35,514 |   |
| Supplemental disclosure of non-cash investing transactions:                   |   |                         |     |   |   |   |   |   |
| Property, plant and equipment additions in accounts payable                   |   | $                            | 91,478   |   |   | $ | 9,799 |   |

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|                                                                                  |   | March 31, 2011 |       |   | Dec. 31, 2010 |   |
|---------------------------------------------------------------------------------------|--------|----------------|------------|--------|---------------|--------|
| Assets                                                                                |   |           |       |   |          |   |
| Current assets                                                                        |   |           |       |   |          |   |
| Cash and cash equivalents                                                             |   | $              | 24,678     |   |          | $      | 32,912 |   |
| Accounts receivable, net                                                              |   |           | 302,830    |   |          |   | 305,469 |   |
| Accounts receivable from affiliates                                                   |   |           | 11,796     |   |          |   | 21,042 |   |
| Accrued unbilled revenues                                                             |   |           | 220,656    |   |          |   | 297,535 |   |
| Inventories                                                                           |   |           | 185,243    |   |          |   | 223,058 |   |
| Regulatory assets                                                                     |   |           | 157,083    |   |          |   | 176,596 |   |
| Deferred income taxes                                                                 |   |           | 22,376     |   |          |   | 13,877 |   |
| Derivative instruments                                                                |   |           | 6,785      |   |          |   | 6,294 |   |
| Prepayments and other                                                                 |   |           | 15,727     |   |          |   | 54,235 |   |
| Total current assets                                                                  |   |           | 947,174    |   |          |   | 1,131,018 |   |
|                                                                                  |   |           |       |   |          |   |   |   |
| Property, plant and equipment, net                                                    |   |           | 9,231,890  |   |          |   | 9,200,556 |   |
|                                                                                  |   |           |       |   |          |   |   |   |
| Other assets                                                                          |   |           |       |   |          |   |   |   |
| Regulatory assets                                                                     |   |           | 840,051    |   |          |   | 824,205 |   |
| Derivative instruments                                                                |   |           | 16,085     |   |          |   | 18,035 |   |
| Other                                                                                 |   |           | 54,775     |   |          |   | 55,016 |   |
| Total other assets                                                                    |   |           | 910,911    |   |          |   | 897,256 |   |
| Total assets                                                                          |   | $              | 11,089,975 |   |          | $      | 11,228,830 |   |
|                                                                                  |   |           |       |   |          |   |   |   |
| Liabilities and Equity                                                                |   |           |       |   |          |   |   |   |
| Current liabilities                                                                   |   |           |       |   |          |   |   |   |
| Current portion of long-term debt                                                     |   | $              | 6,504      |   |          | $      | 6,970 |   |
| Short-term debt                                                                       |   |           | 42,000     |   |          |   | 269,400 |   |
| Accounts payable                                                                      |   |           | 324,552    |   |          |   | 382,380 |   |
| Accounts payable to affiliates                                                        |   |           | 25,394     |   |          |   | 28,270 |   |
| Regulatory liabilities                                                                |   |           | 74,009     |   |          |   | 50,018 |   |
| Taxes accrued                                                                         |   |           | 136,006    |   |          |   | 94,321 |   |
| Accrued interest                                                                      |   |           | 53,077     |   |          |   | 48,866 |   |
| Dividends payable to parent                                                           |   |           | 68,218     |   |          |   | 66,828 |   |
| Derivative instruments                                                                |   |           | 8,465      |   |          |   | 29,047 |   |
| Other                                                                                 |   |           | 97,790     |   |          |   | 100,984 |   |
| Total current liabilities                                                             |   |           | 836,015    |   |          |   | 1,077,084 |   |
|                                                                                  |   |           |       |   |          |   |   |   |
| Deferred credits and other liabilities                                                |   |           |       |   |          |   |   |   |
| Deferred income taxes                                                                 |   |           | 1,596,092  |   |          |   | 1,539,583 |   |
| Deferred investment tax credits                                                       |   |           | 46,671     |   |          |   | 47,338 |   |
| Regulatory liabilities                                                                |   |           | 477,542    |   |          |   | 472,846 |   |
| Asset retirement obligations                                                          |   |           | 74,556     |   |          |   | 72,687 |   |
| Derivative instruments                                                                |   |           | 41,399     |   |          |   | 43,220 |   |
| Customer advances                                                                     |   |           | 240,538    |   |          |   | 244,345 |   |
| Pension and employee benefit obligations                                              |   |           | 245,998    |   |          |   | 303,946 |   |
| Other                                                                                 |   |           | 60,862     |   |          |   | 61,334 |   |
| Total deferred credits and other liabilities                                          |   |           | 2,783,658  |   |          |   | 2,785,299 |   |
|                                                                                  |   |           |       |   |          |   |   |   |
| Commitments and contingent liabilities                                                |   |           |       |   |          |   |   |   |
| Capitalization                                                                        |   |           |       |   |          |   |   |   |
| Long-term debt                                                                        |   |           | 3,228,956  |   |          |   | 3,228,253 |   |
| Common stock – authorized 100 shares of $0.01 par value; outstanding 100 shares |   |           | -          |   |          |   | - |   |
| Additional paid-in capital                                                            |   |           | 3,330,586  |   |          |   | 3,255,586 |   |
| Retained earnings                                                                     |   |           | 903,562    |   |          |   | 875,151 |   |
| Accumulated other comprehensive income                                                |   |           | 7,198      |   |          |   | 7,457 |   |
| Total common stockholder's equity                                                     |   |           | 4,241,346  |   |          |   | 4,138,194 |   |
| Total liabilities and equity                                                          |   | $              | 11,089,975 |   |          | $      | 11,228,830 |   |

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| 1. | Summary of Significant Accounting Policies |
|----|--------------------------------------------|

| 2. | Accounting Pronouncements |
|----|---------------------------|

| 3. | Selected Balance Sheet Data |
|----|-----------------------------|

| (Thousands of Dollars)    |   | March 31, 2011 |       |   | Dec. 31, 2010 |   |
|-------------------------------------|--------|----------------|------------|--------|--------------------|--------|
| Accounts receivable, net            |   |           |       |   |               |   |
| Accounts receivable                 |   | $              | 325,856    |   |               | $      | 329,523 |   |
| Less allowance for bad debts        |   |           | (23,026    | )      |               |   | (24,054 | ) |
|                                |   | $              | 302,830    |   |               | $      | 305,469 |   |
| Inventories                         |   |           |       |   |               |   |   |   |
| Materials and supplies              |   | $              | 51,545     |   |               | $      | 51,615 |   |
| Fuel                                |   |           | 69,454     |   |               |   | 67,187 |   |
| Natural gas                         |   |           | 64,244     |   |               |   | 104,256 |   |
|                                |   | $              | 185,243    |   |               | $      | 223,058 |   |
| Property, plant and equipment, net  |   |           |       |   |               |   |   |   |
| Electric plant                      |   | $              | 9,065,460  |   |               | $      | 9,003,103 |   |
| Natural gas plant                   |   |           | 2,300,768  |   |               |   | 2,284,212 |   |
| Common and other property           |   |           | 759,060    |   |               |   | 757,059 |   |
| Plant to be retired (a)             |   |           | 220,939    |   |               |   | 236,606 |   |
| Construction work in progress       |   |           | 255,944    |   |               |   | 231,636 |   |
| Total property, plant and equipment |   |           | 12,602,171 |   |               |   | 12,512,616 |   |
| Less accumulated depreciation       |   |           | (3,370,281 | )      |               |   | (3,312,060 | ) |
|                                |   | $              | 9,231,890  |   |               | $      | 9,200,556 |   |

| (a)  | In 2009, in accordance with the Colorado Public Utility Commission (CPUC’s) approval of PSCo’s 2007 Colorado resource plan and subsequent rate case decisions, PSCo agreed to early retire its Cameo Units 1 and 2, Arapahoe Units 3 and 4 and Zuni Units 1 and 2 facilities.  In 2010, in response to the Clean Air Clean Jobs Act (CACJA), the CPUC approved the early retirement of Cherokee Units 1, 2 and 3, Arapahoe Unit 3 and Valmont Unit 5 between 2011 and 2017.  Amounts are presented net of accumulated depreciation. |
|-----------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

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| 4. | Income Taxes |
|----|--------------|

| (Millions of Dollars)                    |   | March 31, 2011 |   |   | Dec. 31, 2010 |   |
|----------------------------------------------------|--------|----------------|--------|--------|---------------|--------|
| Unrecognized tax benefit - Permanent tax positions |   | $              | 1.4    |   |          | $      | 1.3 |   |
| Unrecognized tax benefit - Temporary tax positions |   |           | 10.1   |   |          |   | 10.3 |   |
| Unrecognized tax benefit balance                   |   | $              | 11.5   |   |          | $      | 11.6 |   |

| (Millions of Dollars)                               |   | March 31, 2011 |   |   | Dec. 31, 2010 |   |
|---------------------------------------------------------------|--------|----------------|--------|--------|---------------|--------|
| Tax benefits associated with NOL and tax credit carryforwards |   | $              | (7.2   | )      |          | $      | (7.2 | ) |

| 5. | Rate Matters |
|----|--------------|

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|   | · | PSCo rebuttal testimony and staff and intervenor cross answer testimony is due on May 6, 2011; |
|--------|--------|-----------------------------------------------------------------------------------------------------|

|   | · | Hearings are scheduled for late May 2011. |
|--------|--------|-------------------------------------------|

| 6. | Commitments and Contingent Liabilities |
|----|----------------------------------------|

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| 7. | Borrowings and Other Financing Instruments |
|----|--------------------------------------------|

| (Millions of Dollars)                           |   | Three Months Ended March 31, 2011 |   |   | Twelve Months Ended Dec. 31, 2010 |   |
|-----------------------------------------------------------|--------|-----------------------------------|--------|--------|-----------------------------------|--------|
| Borrowing limit                                           |   | $                                 | 700    |   |                              | $      | 675 |   |
| Amount outstanding at period end                     |   |                              | 42     |   |                              |   | 269 |   |
| Average amount outstanding                                |   |                              | 151    |   |                              |   | 49 |   |
| Maximum amount outstanding                                |   |                              | 304    |   |                              |   | 275 |   |
| Weighted average interest rate, computed on a daily basis |   |                              | 0.39   | %      |                              | 0.37   | % |
| Weighted average interest rate at end of period           |   |                              | 0.37   |   |                              |   | 0.42 |   |

|   | · | The credit facility may be increased by up to $100 million. |
|--------|--------|-------------------------------------------------------------|

|   | · | The credit facility has a financial covenant requiring that PSCo’s debt-to-total capitalization ratio be less than or equal to 65 percent.  PSCo was in compliance as its debt-to-total capitalization ratio was 44 percent and 46 percent at March 31, 2011 and Dec. 31, 2010, respectively.  If PSCo does not comply with the covenant, an event of default may be declared, and if not remedied, any outstanding amounts due under the facility can be declared due by the lender. |
|--------|--------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

|   | · | The credit facility has a cross-default provision that provides PSCo will be in default on its borrowings under the facility if it or any of its subsidiaries, comprising 15 percent or more of the consolidated assets, defaults on any indebtedness in an aggregate principal amount exceeding $75 million. |
|--------|--------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

|   | · | The interest rates under the line of credit are based on the Eurodollar rate, plus a borrowing margin based on the applicable credit ratings of 100 to 200 basis points per year. |
|--------|--------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

|   | · | The commitment fees, also based on applicable long-term credit ratings, are calculated on the unused portion of the line of credit at a range of 10 to 35 basis points per year. |
|--------|--------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| Credit Facility |   |   | Drawn (a) |   |   | Available |   |
|-----------------|--------|--------|-----------|--------|--------|-----------|--------|
| $               | 700.0  |   |      | $      | 46.6   |      |   | $ | 653.4 |   |

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| (Millions of Dollars)                           |   | Three Months Ended March 31, 2011 |   |   | Twelve Months Ended Dec. 31, 2010 |   |
|-----------------------------------------------------------|--------|-----------------------------------|--------|--------|-----------------------------------|--------|
| Borrowing limit                                           |   | $                                 | 250    |   |                              | $      | 250 |   |
| Amount outstanding at period end                     |   |                              | -      |   |                              |   | - |   |
| Average amount outstanding                                |   |                              | 3      |   |                              |   | 8 |   |
| Maximum amount outstanding                                |   |                              | 53     |   |                              |   | 84 |   |
| Weighted average interest rate, computed on a daily basis |   |                              | 0.35   | %      |                              |   | 0.33 | % |
| Weighted average interest rate at end of period           |   |                              | N/A    |   |                              |   | N/A |   |

| 8. | Fair Value of Financial Assets and Liabilities |
|----|------------------------------------------------|

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| (Amounts in Thousands) (a) (b)      |   | March 31, 2011 |   |   | Dec. 31, 2010 |   |
|-------------------------------------|--------|---------------------|--------|--------|---------------|--------|
| Megawatt hours (MWh) of electricity |   |                | 3,955  |   |          |   | 2,418 |   |
| MMBtu of natural gas                |   |                | 24,392 |   |          |   | 59,465 |   |
| Gallons of vehicle fuel             |   |                | 338    |   |          |   | 360 |   |

|                                                                               |   | Three Months Ended March 31, |   |
|------------------------------------------------------------------------------------|--------|------------------------------|--------|
| (Thousands of Dollars)                                                   |   | 2011                         |   |   | 2010 |   |
| Accumulated other comprehensive income related to cash flow hedges at Jan. 1  |   | $                            | 7,457  |   |   | $ | 8,101 |   |
| After-tax net unrealized gains related to derivatives accounted for as hedges      |   |                         | 98     |   |   |   | 15 |   |
| After-tax net realized gains on derivative transactions reclassified into earnings |   |                         | (357   | ) |   |   | (123 | ) |
| Accumulated other comprehensive income related to cash flow hedges at March 31     |   | $                            | 7,198  |   |   | $ | 7,993 |   |

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|                                |   | Three Months Ended March 31, 2011 |   |
|-------------------------------------|--------|-----------------------------------|--------|
|                                |   | Fair Value Changes Recognized     |   |   | Pre-Tax Amounts Reclassified into |   |   | Pre-Tax |   |
|                                |   | During the Period in:             |   |   | Income During the Period from: |   |   | Gains |   |
|                                |   | Other                             |   |   | Regulatory |   |   | Other |   |   | Regulatory |   |   | Recognized |   |
|                                |   | Comprehensive                     |   |   | Assets and |   |   | Comprehensive |   |   | Assets and |   |   | During the Period |   |
| (Thousands of Dollars)    |   | Income                            |   |   | Liabilities |   |   | Loss |   |   | Liabilities |   |   | in Income |   |
| Derivatives designated as cash flow |   |                              |   |   |   |   |   |   |   |   |   |   |   |   |   |
| hedges                              |   |                              |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Interest rate                       |   | $                                 | -      |   |   | $ | - |   |   | $ | (576 | )(a) |   | $ | - |   |   | $ | - |   |
| Vehicle fuel and other commodity    |   |                              | 176    |   |   |   | - |   |   |   | (18 | )(c) |   |   | - |   |   |   | - |   |
| Total                               |   | $                                 | 176    |   |   | $ | - |   |   | $ | (594 | ) |   | $ | - |   |   | $ | - |   |
|                                |   |                              |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Other derivative instruments        |   |                              |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Trading commodity                   |   | $                                 | -      |   |   | $ | - |   |   | $ | - |   |   | $ | - |   |   | $ | 245 | (b) |
| Natural gas commodity               |   |                              | -      |   |   |   | (5,354 | ) |   |   | - |   |   |   | 44,482 | (d) |   |   | - |   |
| Total                               |   | $                                 | -      |   |   | $ | (5,354 | ) |   | $ | - |   |   | $ | 44,482 |   |   | $ | 245 |   |

|                                |   | Three Months Ended March 31, 2010 |   |
|-------------------------------------|--------|-----------------------------------|--------|
|                                |   | Fair Value Changes Recognized     |   |   | Pre-Tax Amounts Reclassified into |   |   | Pre-Tax |   |
|                                |   | During the Period in:             |   |   | Income During the Period from: |   |   | Gains (Losses) |   |
|                                |   | Other                             |   |   | Regulatory |   |   | Other |   |   | Regulatory |   |   | Recognized |   |
|                                |   | Comprehensive                     |   |   | Assets and |   |   | Comprehensive |   |   | Assets and |   |   | During the Period |   |
| (Thousands of Dollars)    |   | Income                            |   |   | Liabilities |   |   | Income (Loss) |   |   | Liabilities |   |   | in Income |   |
| Derivatives designated as cash flow |   |                              |   |   |   |   |   |   |   |   |   |   |   |   |   |
| hedges                              |   |                              |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Interest rate                       |   | $                                 | -      |   |   | $ | - |   |   | $ | (576 | )(a) |   | $ | - |   |   | $ | - |   |
| Vehicle fuel and other commodity    |   |                              | 24     |   |   |   | - |   |   |   | 377 | (c) |   |   | - |   |   |   | - |   |
| Total                               |   | $                                 | 24     |   |   | $ | - |   |   | $ | (199 | ) |   | $ | - |   |   | $ | - |   |
|                                |   |                              |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Other derivative instruments        |   |                              |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Trading commodity                   |   | $                                 | -      |   |   | $ | - |   |   | $ | - |   |   | $ | - |   |   | $ | (249 | )(b) |
| Natural gas commodity               |   |                              | -      |   |   |   | (27,564 | ) |   |   | - |   |   |   | 3,637 | (d) |   |   | - |   |
| Vehicle fuel and other commodity    |   |                              | -      |   |   |   | - |   |   |   | - |   |   |   | - |   |   |   | 50 | (b) |
| Total                               |   | $                                 | -      |   |   | $ | (27,564 | ) |   | $ | - |   |   | $ | 3,637 |   |   | $ | (199 | ) |

| (a)  | Recorded to interest charges. |
|-----------|-------------------------------|

| (b)  | Recorded to electric operating revenues.  Portions of these total gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue, as appropriate. |
|-----------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (c)  | Recorded to O&M expenses. |
|-----------|-------------------------------|

| (d)  | Recorded to cost of natural gas sold and transported; these derivative settlement gains and losses are shared with natural gas customers through purchased natural gas cost-recovery mechanisms, and reclassified out of income as regulatory assets and liabilities, as appropriate. |
|-----------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

----

Table of Contents

|                                        |   | March 31, 2011 |   |
|---------------------------------------------|--------|----------------|--------|
|                                        |   | Fair Value     |   |   |   |   |   |   |   |   |   |   |
|                                        |   |           |   |   |   |   |   |   |   |   | Fair Value |   |   | Counterparty |   |   |   |   |
| (Thousands of Dollars)            |   | Level 1   |   |   | Level 2 |   |   | Level 3 |   |   | Total |   |   | Netting (b) |   |   | Total |   |
| Current derivative assets                   |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Derivatives designated as cash flow hedges: |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Vehicle fuel and other commodity            |   | $              | -      |   |   | $ | 107 |   |   | $ | - |   |   | $ | 107 |   |   | $ | - |   |   | $ | 107 |   |
| Other derivative instruments:               |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Trading commodity                           |   |           | 13     |   |   |   | 7,712 |   |   |   | - |   |   |   | 7,725 |   |   |   | (4,285 | ) |   |   | 3,440 |   |
| Natural gas commodity                       |   |           | -      |   |   |   | 1,417 |   |   |   | - |   |   |   | 1,417 |   |   |   | (908 | ) |   |   | 509 |   |
| Total current derivative assets             |   | $              | 13     |   |   | $ | 9,236 |   |   | $ | - |   |   | $ | 9,249 |   |   | $ | (5,193 | ) |   |   | 4,056 |   |
| Purchased power agreements (a)              |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | 2,729 |   |
| Current derivative instruments              |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | $ | 6,785 |   |
| Noncurrent derivative assets                |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Derivatives designated as cash flow hedges: |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Vehicle fuel and other commodity            |   | $              | -      |   |   | $ | 183 |   |   | $ | - |   |   | $ | 183 |   |   | $ | - |   |   | $ | 183 |   |
| Other derivative instruments:               |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Trading commodity                           |   |           | -      |   |   |   | 6,198 |   |   |   | - |   |   |   | 6,198 |   |   |   | (2,029 | ) |   |   | 4,169 |   |
| Total noncurrent derivative assets          |   | $              | -      |   |   | $ | 6,381 |   |   | $ | - |   |   | $ | 6,381 |   |   | $ | (2,029 | ) |   |   | 4,352 |   |
| Purchased power agreements (a)              |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | 11,733 |   |
| Noncurrent derivative instruments           |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | $ | 16,085 |   |
|                                        |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
|                                        |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Current derivative liabilities              |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Other derivative instruments:               |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Trading commodity                           |   | $              | 59     |   |   | $ | 7,111 |   |   | $ | - |   |   | $ | 7,170 |   |   | $ | (5,423 | ) |   | $ | 1,747 |   |
| Natural gas commodity                       |   |           | -      |   |   |   | 1,886 |   |   |   | - |   |   |   | 1,886 |   |   |   | (908 | ) |   |   | 978 |   |
| Total current derivative liabilities        |   | $              | 59     |   |   | $ | 8,997 |   |   | $ | - |   |   | $ | 9,056 |   |   | $ | (6,331 | ) |   |   | 2,725 |   |
| Purchased power agreements (a)              |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | 5,740 |   |
| Current derivative instruments              |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | $ | 8,465 |   |
| Noncurrent derivative liabilities           |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Other derivative instruments:               |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Trading commodity                           |   | $              | -      |   |   | $ | 5,190 |   |   | $ | - |   |   | $ | 5,190 |   |   | $ | (2,029 | ) |   | $ | 3,161 |   |
| Total noncurrent derivative liabilities     |   | $              | -      |   |   | $ | 5,190 |   |   | $ | - |   |   | $ | 5,190 |   |   | $ | (2,029 | ) |   |   | 3,161 |   |
| Purchased power agreements (a)              |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | 38,238 |   |
| Noncurrent derivative instruments           |   |           |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | $ | 41,399 |   |

| (a)  | In 2003, as a result of implementing new guidance on the normal purchase exception for derivative accounting, PSCo began recording several long-term purchased power agreements at fair value due to accounting requirements related to underlying price adjustments.  As these purchases are recovered through normal regulatory recovery mechanisms in the respective jurisdictions, the changes in fair value for these contracts were offset by regulatory assets and liabilities.  During 2006, PSCo qualified these contracts under the normal purchase exception.  Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities. |
|-----------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (b)  | The accounting for derivatives and hedging permits the netting of receivables and payables for derivatives and related collateral amounts when a legally enforceable master netting agreement exists between PSCo and a counterparty.  A master netting agreement is an agreement between two parties who have multiple contracts with each other that provides for the net settlement of all contracts in the event of default on or termination of any one contract. |
|-----------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

----

Table of Contents

| (Thousands of Dollars)                                  |   |   |   |
|-------------------------------------------------------------------|--------|--------|--------|
| Trading commodity derivatives not designated as cash flow hedges: |   |   |   |
| Current assets                                                    |   | $      | 1,740  |   |
| Noncurrent assets                                                 |   |   | 4,988  |   |
| Current liabilities                                               |   |   | (1,265 | ) |
| Noncurrent liabilities                                            |   |   | (2,891 | ) |
| Total                                                             |   | $      | 2,572  |   |

|                                        |   | Dec. 31, 2010 |   |
|---------------------------------------------|--------|---------------|--------|
|                                        |   | Fair Value    |   |   |   |   |   |   |   |   |   |   |
|                                        |   |          |   |   |   |   |   |   |   |   | Fair Value |   |   | Counterparty |   |   |   |   |
| (Thousands of Dollars)            |   | Level 1  |   |   | Level 2 |   |   | Level 3 |   |   | Total |   |   | Netting (b) |   |   | Total |   |
| Current derivative assets                   |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Derivatives designated as cash flow hedges: |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Vehicle fuel and other commodity            |   | $             | -      |   |   | $ | 56 |   |   | $ | - |   |   | $ | 56 |   |   | $ | - |   |   | $ | 56 |   |
| Other derivative instruments:               |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Trading commodity                           |   |          | -      |   |   |   | 5,765 |   |   |   | - |   |   |   | 5,765 |   |   |   | (2,633 | ) |   |   | 3,132 |   |
| Natural gas commodity                       |   |          | -      |   |   |   | 1,396 |   |   |   | - |   |   |   | 1,396 |   |   |   | (1,019 | ) |   |   | 377 |   |
| Total current derivative assets             |   | $             | -      |   |   | $ | 7,217 |   |   | $ | - |   |   | $ | 7,217 |   |   | $ | (3,652 | ) |   |   | 3,565 |   |
| Purchased power agreements (a)              |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | 2,729 |   |
| Current derivative instruments              |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | $ | 6,294 |   |
| Noncurrent derivative assets                |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Derivatives designated as cash flow hedges: |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Vehicle fuel and other commodity            |   | $             | -      |   |   | $ | 68 |   |   | $ | - |   |   | $ | 68 |   |   | $ | - |   |   | $ | 68 |   |
| Other derivative instruments:               |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Trading commodity                           |   |          | -      |   |   |   | 6,770 |   |   |   | - |   |   |   | 6,770 |   |   |   | (2,118 | ) |   |   | 4,652 |   |
| Natural gas commodity                       |   |          | -      |   |   |   | 1,111 |   |   |   | - |   |   |   | 1,111 |   |   |   | (211 | ) |   |   | 900 |   |
| Total noncurrent derivative assets          |   | $             | -      |   |   | $ | 7,949 |   |   | $ | - |   |   | $ | 7,949 |   |   | $ | (2,329 | ) |   |   | 5,620 |   |
| Purchased power agreements (a)              |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | 12,415 |   |
| Noncurrent derivative instruments           |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | $ | 18,035 |   |

----

Table of Contents

|                                    |   | Dec. 31, 2010 |   |
|-----------------------------------------|--------|---------------|--------|
|                                    |   | Fair Value    |   |   |   |   |   |   |   |   |   |   |
|                                    |   |          |   |   |   |   |   |   |   |   | Fair Value |   |   | Counterparty |   |   |   |   |
| (Thousands of Dollars)        |   | Level 1  |   |   | Level 2 |   |   | Level 3 |   |   | Total |   |   | Netting (b) |   |   | Total |   |
| Current derivative liabilities          |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Other derivative instruments:           |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Trading commodity                       |   | $             | -      |   |   | $ | 5,192 |   |   | $ | - |   |   | $ | 5,192 |   |   | $ | (2,669 | ) |   | $ | 2,523 |   |
| Natural gas commodity                   |   |          | -      |   |   |   | 41,753 |   |   |   | - |   |   |   | 41,753 |   |   |   | (20,969 | ) |   |   | 20,784 |   |
| Total current derivative liabilities    |   | $             | -      |   |   | $ | 46,945 |   |   | $ | - |   |   | $ | 46,945 |   |   | $ | (23,638 | ) |   |   | 23,307 |   |
| Purchased power agreements (a)          |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | 5,740 |   |
| Current derivative instruments          |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | $ | 29,047 |   |
| Noncurrent derivative liabilities       |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Other derivative instruments:           |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Trading commodity                       |   | $             | -      |   |   | $ | 5,526 |   |   | $ | - |   |   | $ | 5,526 |   |   | $ | (2,118 | ) |   | $ | 3,408 |   |
| Natural gas commodity                   |   |          | -      |   |   |   | 350 |   |   |   | - |   |   |   | 350 |   |   |   | (211 | ) |   |   | 139 |   |
| Total noncurrent derivative liabilities |   | $             | -      |   |   | $ | 5,876 |   |   | $ | - |   |   | $ | 5,876 |   |   | $ | (2,329 | ) |   |   | 3,547 |   |
| Purchased power agreements (a)          |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | 39,673 |   |
| Noncurrent derivative instruments       |   |          |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   | $ | 43,220 |   |

| (a)  | In 2003, as a result of implementing new guidance on the normal purchase exception for derivative accounting, PSCo began recording several long-term purchased power agreements at fair value due to accounting requirements related to underlying price adjustments.  As these purchases are recovered through normal regulatory recovery mechanisms in the respective jurisdictions, the changes in fair value for these contracts were offset by regulatory assets and liabilities.  During 2006, PSCo qualified these contracts under the normal purchase exception.  Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities. |
|-----------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (b)  | The accounting for derivatives and hedging permits the netting of receivables and payables for derivatives and related collateral amounts when a legally enforceable master netting agreement exists between PSCo and a counterparty.  A master netting agreement is an agreement between two parties who have multiple contracts with each other that provides for the net settlement of all contracts in the event of default on or termination of any one contract. |
|-----------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (Thousands of Dollars) |   | March 31, 2010 |   |
|----------------------------------|--------|----------------|--------|
| Balance at Jan. 1                |   | $              | 804    |   |
| Purchases                        |   |           | (55    | ) |
| Settlements                      |   |           | (94    | ) |
| Transfers out of Level 3         |   |           | (2,572 | ) |
| Gains recognized in earnings (a) |   |           | 2,248  |   |
| Balance at March 31              |   | $              | 331    |   |

|                                      |   | March 31, 2011 |      |   | Dec. 31, 2010 |   |
|-------------------------------------------|--------|----------------|-----------|--------|---------------|--------|
|                                      |   | Carrying       |      |   |          |   |   | Carrying |   |   |   |   |
| (Thousands of Dollars)          |   | Amount         |      |   | Fair Value    |   |   | Amount |   |   | Fair Value |   |
| Long-term debt, including current portion |   | $              | 3,235,460 |   |          | $      | 3,487,803 |   |   | $ | 3,235,223 |   |   | $ | 3,531,729 |   |

----

Table of Contents

| 9.  | Other Income, Net |
|----------|-------------------|

|                             |   | Three Months Ended March 31, |   |
|----------------------------------|--------|------------------------------|--------|
| (Thousands of Dollars) |   | 2011                         |   |   | 2010 |   |
| Interest income                  |   | $                            | 1,303  |   |   | $ | 378 |   |
| Other nonoperating income        |   |                         | 607    |   |   |   | 431 |   |
| Insurance policy expenses        |   |                         | (247   | ) |   |   | (253 | ) |
| Other income, net                |   | $                            | 1,663  |   |   | $ | 556 |   |

| 10.  | Segment Information |
|-----------|---------------------|

| · | PSCo’s regulated electric utility segment generates, transmits and distributes electricity in Colorado.  In addition, this segment includes sales for resale and provides wholesale transmission service to various entities in the United States.  Regulated electric utility also includes PSCo’s commodity trading operations. |
|--------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| · | PSCo’s regulated natural gas utility segment transports, stores and distributes natural gas in portions of Colorado. |
|--------|----------------------------------------------------------------------------------------------------------------------------|

| · | Revenues from operating segments not included above are below the necessary quantitative thresholds and are therefore included in the all other category.  Those primarily include steam revenue, appliance repair services and nonutility real estate activities. |
|--------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

|                                       |   | Regulated |    |   | Regulated        |   |    | All    |   |   | Reconciling  |   |   | Consolidated |   |
|--------------------------------------------|--------|-----------|---------|--------|------------------|--------|---------|--------|--------|--------|--------------|--------|--------|--------------|--------|
| (Thousands of Dollars)           |   | Electric  |    |   | Natural Gas |   |    | Other  |   |   | Eliminations |   |   | Total        |   |
| Three Months Ended March 31, 2011          |   |      |    |   |             |   |    |   |   |   |         |   |   |         |   |
| Operating revenues from external customers |   | $         | 704,153 |   |             | $      | 428,191 |   |   | $      | 12,103       |   |   | $            | -      |   |   | $ | 1,144,447 |   |
| Intersegment revenues                      |   |      | 114     |   |             |   | 46      |   |   |   | -            |   |   |         | (160   | ) |   |   | - |   |
| Total revenues                             |   | $         | 704,267 |   |             | $      | 428,237 |   |   | $      | 12,103       |   |   | $            | (160   | ) |   | $ | 1,144,447 |   |
| Net income                                 |   | $         | 65,715  |   |             | $      | 28,878  |   |   | $      | 2,037        |   |   | $            | -      |   |   | $ | 96,630 |   |

----

Table of Contents

|                                       |   | Regulated |    |   | Regulated        |   |    | All    |   |   | Reconciling  |   |   | Consolidated |   |
|--------------------------------------------|--------|-----------|---------|--------|------------------|--------|---------|--------|--------|--------|--------------|--------|--------|--------------|--------|
| (Thousands of Dollars)           |   | Electric  |    |   | Natural Gas |   |    | Other  |   |   | Eliminations |   |   | Total        |   |
| Three Months Ended March 31, 2010          |   |      |    |   |             |   |    |   |   |   |         |   |   |         |   |
| Operating revenues from external customers |   | $         | 723,634 |   |             | $      | 466,283 |   |   | $      | 12,780       |   |   | $            | -      |   |   | $ | 1,202,697 |   |
| Intersegment revenues                      |   |      | 1,012   |   |             |   | 72      |   |   |   | -            |   |   |         | (1,084 | ) |   |   | - |   |
| Total revenues                             |   | $         | 724,646 |   |             | $      | 466,355 |   |   | $      | 12,780       |   |   | $            | (1,084 | ) |   | $ | 1,202,697 |   |
| Net income (loss)                          |   | $         | 57,354  |   |             | $      | 34,674  |   |   | $      | (7,778       | )      |   | $            | -      |   |   | $ | 84,250 |   |

| 11.  | Comprehensive Income |
|-----------|----------------------|

|                                                                               |   | Three Months Ended March 31, |   |
|------------------------------------------------------------------------------------|--------|------------------------------|--------|
| (Thousands of Dollars)                                                   |   | 2011                         |   |   | 2010 |   |
| Net income                                                                         |   | $                            | 96,630 |   |   | $ | 84,250 |   |
| Other comprehensive (loss) income:                                                 |   |                         |   |   |   |   |   |   |
| After-tax net unrealized gains related to derivatives accounted for as hedges      |   |                         | 98     |   |   |   | 15 |   |
| After-tax net realized gains on derivative transactions reclassified into earnings |   |                         | (357   | ) |   |   | (123 | ) |
| Other comprehensive loss                                                           |   |                         | (259   | ) |   |   | (108 | ) |
| Comprehensive income                                                               |   | $                            | 96,371 |   |   | $ | 84,142 |   |

| 12.  | Benefit Plans and Other Postretirement Benefits |
|-----------|-------------------------------------------------|

|                                                        |   | Three Months Ended March 31, |    |
|-------------------------------------------------------------|--------|------------------------------|---------|
|                                                        |   | 2011                         |    |   | 2010 |   |   | 2011 |   |   | 2010 |   |
| (Thousands of Dollars)                            |   | Pension Benefits             |    |   | Postretirement Health Care Benefits |   |
| Xcel Energy                                                 |   |                         |    |   |   |   |   |   |   |   |   |   |
| Service cost                                                |   | $                            | 18,112  |   |   | $ | 17,618 |   |   | $ | 1,315 |   |   | $ | 1,038 |   |
| Interest cost                                               |   |                         | 39,915  |   |   |   | 40,652 |   |   |   | 10,551 |   |   |   | 10,529 |   |
| Expected return on plan assets                              |   |                         | (55,286 | ) |   |   | (58,124 | ) |   |   | (7,968 | ) |   |   | (7,134 | ) |
| Amortization of transition obligation                       |   |                         | -       |   |   |   | - |   |   |   | 3,611 |   |   |   | 3,611 |   |
| Amortization of prior service cost (credit)                 |   |                         | 5,633   |   |   |   | 5,164 |   |   |   | (1,233 | ) |   |   | (1,233 | ) |
| Amortization of net loss                                    |   |                         | 18,729  |   |   |   | 11,024 |   |   |   | 3,343 |   |   |   | 2,709 |   |
| Net periodic benefit cost                                   |   |                         | 27,103  |   |   |   | 16,334 |   |   |   | 9,619 |   |   |   | 9,520 |   |
| Costs not recognized and additional cost recognized due     |   |                         |    |   |   |   |   |   |   |   |   |   |   |   |   |   |
| to the effects of regulation                           |   |                         | (7,885  | ) |   |   | (7,326 | ) |   |   | 973 |   |   |   | 973 |   |
| Net benefit cost recognized for financial reporting         |   | $                            | 19,218  |   |   | $ | 9,008 |   |   | $ | 10,592 |   |   | $ | 10,493 |   |
|                                                        |   |                         |    |   |   |   |   |   |   |   |   |   |   |   |   |   |
| PSCo                                                        |   |                         |    |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Net periodic benefit cost                                   |   | $                            | 7,210   |   |   | $ | 3,323 |   |   | $ | 5,570 |   |   | $ | 5,513 |   |
| Additional cost recognized due to the effects of regulation |   |                         | -       |   |   |   | - |   |   |   | 973 |   |   |   | 973 |   |
| Net benefit cost recognized for financial reporting         |   | $                            | 7,210   |   |   | $ | 3,323 |   |   | $ | 6,543 |   |   | $ | 6,486 |   |

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|                              |   | Three Months Ended March 31, |   |
|-----------------------------------|--------|------------------------------|--------|
| (Millions of Dollars)             |   | 2011                         |   | 2010 |   |
| Electric revenues                 |   | $                            | 704    |   |   | $ | 724 |   |
| Electric fuel and purchased power |   |                         | (324   | ) |   |   | (374 | ) |
| Electric margin                   |   | $                            | 380    |   |   | $ | 350 |   |

| (Millions of Dollars)                                    |   | 2011 vs. 2010 |   |
|----------------------------------------------------------|--------|---------------|--------|
| Fuel and purchased power cost recovery                   |   | $             | (51    | ) |
| Retail rate increase, offset by impact of seasonal rates |   |          | (4     | ) |
| Firm wholesale                                           |   |          | (3     | ) |
| Revenue requirements for PSCo generation acquisition (a) |   |          | 34     |   |
| Renewable energy credit sales                            |   |          | 2      |   |
| Service and facility fees                                |   |          | 2      |   |
| Total decrease in electric revenues                      |   | $             | (20    | ) |

| (Millions of Dollars)                                    |   | 2011 vs. 2010 |   |
|----------------------------------------------------------|--------|---------------|--------|
| Revenue requirements for PSCo generation acquisition (a) |   | $             | 34     |   |
| Service and facility fees                                |   |          | 2      |   |
| Retail rate increase, offset by impact of seasonal rates |   |          | (4     | ) |
| Renewable energy credit sales                            |   |          | (2     | ) |
| Total increase in electric margin                        |   | $             | 30     |   |

| (a)  | The increase in revenue requirements for PSCo generation reflects the acquisition of the Rocky Mountain and Blue Spruce natural gas facilities in 2010.  These revenue requirements are partially offset by increased O&M expense, depreciation expense, property taxes and financing costs. |
|-----------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

|                                     |   | Three Months Ended March 31, |   |
|------------------------------------------|--------|------------------------------|--------|
| (Millions of Dollars)                    |   | 2011                         |   |   | 2010 |   |
| Natural gas revenues                     |   | $                            | 428    |   |   | $ | 466 |   |
| Cost of natural gas sold and transported |   |                         | (305   | ) |   |   | (341 | ) |
| Natural gas margin                       |   | $                            | 123    |   |   | $ | 125 |   |

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| (Millions of Dollars)                            |   | 2011 vs. 2010 |   |
|--------------------------------------------------|--------|---------------|--------|
| Purchased natural gas adjustment clause recovery |   | $             | (36    | ) |
| Retail sales decrease (excluding weather impact) |   |          | (2     | ) |
| Total decrease in natural gas revenues           |   | $             | (38    | ) |

| (Millions of Dollars)                            |   | 2011 vs. 2010 |   |
|--------------------------------------------------|--------|---------------|--------|
| Retail sales decrease (excluding weather impact) |   | $             | (2     | ) |
| Total decrease in natural gas margin             |   | $             | (2     | ) |

| Operating and Maintenance Expenses — O&M expenses increased by approximately $15.0 million, or 9.6 percent, for the first three months of 2011, compared with the first three months of 2010.  The following summarizes the components of the changes for the three months ended March 31: |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| (Millions of Dollars)                                |   | 2011 vs. 2010 |   |
|------------------------------------------------------|--------|---------------|--------|
| Higher plant generation costs                        |   | $             | 6      |   |
| Higher employee benefit costs                        |   |          | 4      |   |
| Higher labor costs                                   |   |          | 3      |   |
| Higher contract labor costs                          |   |          | 2      |   |
| Total increase in operating and maintenance expenses |   | $             | 15     |   |

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|   | · | Shutdown Cherokee Units 1 and 2 in 2011 and Cherokee Unit 3 (365 MW in total) by the end of 2015, after a new natural gas combined-cycle unit is built at Cherokee Station (569 MW); |
|--------|--------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

|   | · | Fuel-switch Cherokee Unit 4 (352 MW) to natural gas by 2017; |
|--------|--------|--------------------------------------------------------------|

|   | · | Shutdown Arapahoe Unit 3 (45 MW) and fuel-switch Unit 4 (111 MW) in 2014 to natural gas; |
|--------|--------|------------------------------------------------------------------------------------------|

|   | · | Shutdown Valmont Unit 5 (186 MW) in 2017; |
|--------|--------|-------------------------------------------|

|   | · | Install SCR for controlling NOx and a scrubber for controlling SO2 on Pawnee Station in 2014; |
|--------|--------|-----------------------------------------------------------------------------------------------|

|   | · | Install SCR on Hayden Unit 1 in 2015 and Hayden Unit 2 in 2016; and |
|--------|--------|---------------------------------------------------------------------|

|   | · | Convert Cherokee Unit 2 and Arapahoe Unit 3 to synchronous condensers to support the transmission system. |
|--------|--------|-----------------------------------------------------------------------------------------------------------|

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Item 

Item 

Item 1A — Risk Factors

Item 

| 3.01*  |   | Amended and Restated Articles of Incorporation dated July 15, 1998 (Form 10-K, Dec. 31, 1998, Exhibit 3(a)(1)).                                                                                                                                                                                                                                                                                                                                   |
|--------|--------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| 3.02*  |   | By-laws dated Nov. 20, 1997 (For 10-K, Dec. 31, 1997, Exhibit 3(b)(1)).                                                                                                                                                                                                                                                                                                                                                                                |
| 10.01* |   | Credit Agreement, dated as of March 17, 2011 among PSCo as Borrower, the several lenders from time to time parties thereto, JPMorgan Chase Bank, N.A., as Administrative Agent, Bank of America, N.A., and Barclays Capital, the investment banking division of Barclays Bank Plc, as Syndication Agents, and Wells Fargo Bank, National Association, as Documentation Agent (Exhibit 99.04 to Form 8-K of Xcel Energy, file number 001-03034, dated March 23, 2011). |
| 10.02* |   | Stock Equivalent Plan for Non-Employee Directors of Xcel Energy as amended and restated effective Feb. 23, 2011 (Appendix A to the Xcel Energy Definitive Proxy Statement (file no. 001-03034) filed April 5, 2011).                                                                                                                                                                                                                                                  |
| 31.01  |   | Principal Executive Officer’s and Principal Financial Officer’s certifications pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002.                                                                                                                                                                                                                                                        |
| 32.01  |   | Certification pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.                                                                                                                                                                                                                                                                                                                                     |
| 99.01  |   | Statement pursuant to Private Securities Litigation Reform Act of 1995.                                                                                                                                                                                                                                                                                                                                                                                               |

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SIGNATURES

|        | Public Service Company of Colorado         |
|-------------|--------------------------------------------|
| May 2, 2011 |                                       |
| By:         | /s/ TERESA S. MADDEN                       |
|        | Teresa S. Madden                           |
|        | Vice President and Controller              |
|        |                                       |
|        | /s/ DAVID M. SPARBY                        |
|        | David M. Sparby                            |
|        | Vice President and Chief Financial Officer |

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