----

|         |                                                                                                                                              |
|---------|----------------------------------------------------------------------------------------------------------------------------------------------|
| • | Year-over-year total production increase of 34 percent to 8.9 million barrels of oil equivalent (MMBoe) or approximately 99,000 Boe per day. |

|         |                                                                                                                                    |
|---------|------------------------------------------------------------------------------------------------------------------------------------|
| • | Year-over-year oil production increase of 51 percent to 3.8 million barrels (MMBbls), representing 43 percent of total production. |

|         |                                                                                                                                                                      |
|---------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| • | Total crude oil, natural gas and NGLs sales of approximately $305 million, a 61 percent increase compared to first quarter 2017 sales of approximately $190 million. |

|         |                                                                                                                                                              |
|---------|--------------------------------------------------------------------------------------------------------------------------------------------------------------|
| • | Net cash from operating activities of approximately $205 million, a 47 percent increase compared to first quarter 2017 levels of approximately $140 million. |

|         |                                                                                                                                                                                |
|---------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| • | Completed the previously disclosed sale of Utica Shale assets and amendment to an existing Wattenberg oil gathering agreement for total proceeds of approximately $65 million. |

|         |                                                                                                                                                                                                                                                        |
|---------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| • | The Company recently executed a firm, long-term sales agreement beginning in June 2018 that provides takeaway capacity for the majority of its 2018 and 2019 Delaware basin oil production and diversifies price exposure towards a Brent-based index. |

----

----

----

|                              |
|------------------------------|
|                              |  |  |  |  |  |  |  |  |  |  |
|                         | Three Months Ended March 31, |
|                         | 2018 |   | 2017 |   | Percent Change |
|                         |   |   |   |   |   |
| Crude oil (MBbls)            |   |   |   |   |   |
| Wattenberg Field             | 2,881 |  |   | 2,142 |  |   | 34.5 |  % |
| Delaware Basin               | 871 |  |   | 275 |  |   | * |  |
| Utica Shale                  | 46 |  |   | 91 |  |   | (49.5 | )% |
| Total                        | 3,798 |  |   | 2,508 |  |   | 51.4 |  % |
|                         |   |   |   |   |   |
| Weighted-Average Sales Price | $ | 59.62 |  |   | $ | 49.04 |  |   | 21.6 |  % |
|                         |   |   |   |   |   |
| Natural gas (MMcf)           |   |   |   |   |   |
| Wattenberg Field             | 15,524 |  |   | 13,714 |  |   | 13.2 |  % |
| Delaware Basin               | 3,649 |  |   | 1,246 |  |   | * |  |
| Utica Shale                  | 414 |  |   | 624 |  |   | (33.7 | )% |
| Total                        | 19,587 |  |   | 15,584 |  |   | 25.7 |  % |
|                         |   |   |   |   |   |
| Weighted-Average Sales Price | $ | 1.97 |  |   | $ | 2.37 |  |   | (16.9 | )% |
|                         |   |   |   |   |   |
| NGLs (MBbls)                 |   |   |   |   |   |
| Wattenberg Field             | 1,428 |  |   | 1,358 |  |   | 5.2 |  % |
| Delaware Basin               | 383 |  |   | 131 |  |   | * |  |
| Utica Shale                  | 35 |  |   | 54 |  |   | (35.2 | )% |
| Total                        | 1,846 |  |   | 1,543 |  |   | 19.6 |  % |
|                         |   |   |   |   |   |
| Weighted-Average Sales Price | $ | 21.80 |  |   | $ | 19.29 |  |   | 13.0 |  % |
|                         |   |   |   |   |   |
| Crude oil equivalent (MBoe)  |   |   |   |   |   |
| Wattenberg Field             | 6,896 |  |   | 5,786 |  |   | 19.2 |  % |
| Delaware Basin               | 1,862 |  |   | 613 |  |   | * |  |
| Utica Shale                  | 150 |  |   | 249 |  |   | (39.8 | )% |
| Total                        | 8,908 |  |   | 6,648 |  |   | 34.0 |  % |
|                         |   |   |   |   |   |
| Weighted-Average Sales Price | $ | 34.26 |  |   | $ | 28.53 |  |   | 20.1 |  % |

----

|                                                   |
|---------------------------------------------------|
|                                                   |  |  |  |  |  |  |  |
|                                              | Three Months EndedMarch 31, |
|                                              | 2018 |   | 2017 |
|                                              |   |   |   |
| Lease operating expenses                          | $ | 29.6 |  |   | $ | 19.8 |  |
| Production taxes                                  | 20.2 |  |   | 12.4 |  |
| Transportation, gathering and processing expenses | 7.3 |  |   | 5.9 |  |
| Total                                             | $ | 57.1 |  |   | $ | 38.1 |  |

|                                                           |
|-----------------------------------------------------------|
|                                                           |  |  |  |  |  |  |  |
|                                                      | Three Months EndedMarch 31, |
|                                                      | 2018 |   | 2017 |
|                                                      |   |   |   |
| Lease operating expenses per Boe                          | $ | 3.33 |  |   | $ | 2.98 |  |
| Production taxes per Boe                                  | 2.26 |  |   | 1.87 |  |
| Transportation, gathering and processing expenses per Boe | 0.82 |  |   | 0.89 |  |
| Total per Boe                                             | $ | 6.41 |  |   | $ | 5.74 |  |

----

|                                                                |
|----------------------------------------------------------------|
|                                                                |  |  |  |  |  |  |
|                                                           | Low | High |
| Production (MMBoe)                                             | 38.0 |  | 42.0 |  |
| Capital Expenditures (millions)                                | $ | 850 |  | $ | 920 |  |
|                                                           |   |   |
| Operating Expenses                                             |
| Lease operating expense ($/Boe)                                | $ | 2.75 |  | $ | 3.00 |  |
| Transportation, gathering and processing expenses ($/Boe)      | $ | 0.60 |  | $ | 0.80 |  |
| Production taxes (% of Crude oil, natural gas & NGL sales) | 6 | % | 8 | % |
| General and administrative expense ($/Boe)                     | $ | 3.40 |  | $ | 3.70 |  |
| Estimated Price Realizations (% of NYMEX) (excludes TGP)       |
| Crude oil                                                      | 91% | 95% |
| Natural gas                                                    | 55% | 60% |
| NGLs                                                           | 30% | 35% |

----

|                                      |
|--------------------------------------|
|                                      |  |  |  |  |  |  |  |
| Adjusted Cash Flows from Operations  |
|                                 | Three Months Ended  March 31, |
|                                 | 2018 |   | 2017 |
| Adjusted cash flows from operations: |   |   |   |
| Net cash from operating activities   | $ | 205.1 |  |   | $ | 139.5 |  |
| Changes in assets and liabilities    | (30.2 | ) |   | (25.8 | ) |
| Adjusted cash flows from operations  | $ | 174.9 |  |   | $ | 113.7 |  |

|                                                     |
|-----------------------------------------------------|
|                                                     |  |  |  |  |  |  |  |
| Adjusted Net Income (Loss)                          |
|                                                | Three Months Ended  March 31, |
|                                                | 2018 |   | 2017 |
| Adjusted net income (loss):                         |   |   |   |
| Net income (loss)                                   | $ | (13.1 | ) |   | $ | 46.1 |  |
| (Gain) loss on commodity derivative instruments     | 47.2 |  |   | (80.7 | ) |
| Net settlements on commodity derivative instruments | (26.0 | ) |   | 0.5 |  |
| Tax effect of above adjustments                     | (5.1 | ) |   | 30.0 |  |
| Adjusted net income (loss)                          | $ | 3.0 |  |   | $ | (4.1 | ) |
| Weighted-average diluted shares outstanding         | 66.0 |  |   | 66.1 |  |
| Adjusted diluted earnings per share                 | $ | 0.05 |  |   | $ | (0.06 | ) |

----

|                                                     |
|-----------------------------------------------------|
|                                                     |  |  |  |  |  |  |  |
| Adjusted EBITDAX                                    |
|                                                | Three Months Ended  March 31, |
|                                                | 2018 |   | 2017 |
| Net income (loss) to adjusted EBITDAX:              |   |   |   |
| Net income (loss)                                   | $ | (13.1 | ) |   | $ | 46.1 |  |
| (Gain) loss on commodity derivative instruments     | 47.2 |  |   | (80.7 | ) |
| Net settlements on commodity derivative instruments | (26.0 | ) |   | 0.5 |  |
| Non-cash stock-based compensation                   | 5.3 |  |   | 4.5 |  |
| Interest expense, net                               | 17.4 |  |   | 19.2 |  |
| Income tax expense (benefit)                        | (4.6 | ) |   | 26.3 |  |
| Impairment of properties and equipment              | 33.2 |  |   | 2.2 |  |
| Exploration, geologic, and geophysical expense      | 2.6 |  |   | 1.0 |  |
| Depreciation, depletion, and amortization           | 126.8 |  |   | 109.3 |  |
| Accretion of asset retirement obligations           | 1.3 |  |   | 1.8 |  |
| Adjusted EBITDAX                                    | $ | 190.1 |  |   | $ | 130.2 |  |
|                                                |   |   |   |
| Cash from operating activities to adjusted EBITDAX: |   |   |   |
| Net cash from operating activities                  | $ | 205.1 |  |   | $ | 139.5 |  |
| Interest expense, net                               | 17.4 |  |   | 19.2 |  |
| Amortization of debt discount and issuance costs    | (3.2 | ) |   | (3.2 | ) |
| Gain (loss) on sale of properties and equipment     | (1.4 | ) |   | 0.2 |  |
| Exploration, geologic, and geophysical expense      | 2.6 |  |   | 1.0 |  |
| Other                                               | (0.2 | ) |   | (0.7 | ) |
| Changes in assets and liabilities                   | (30.2 | ) |   | (25.8 | ) |
| Adjusted EBITDAX                                    | $ | 190.1 |  |   | $ | 130.2 |  |

----

|                                                    |
|----------------------------------------------------|
|                                                    |  |  |  |  |  |  |  |
|                                               | Three Months Ended  March 31, |
|                                               | 2018 |   | 2017 |
|                                               |   |   |   |
| Revenues                                           |   |   |   |
| Crude oil, natural gas, and NGLs sales             | $ | 305,225 |  |   | $ | 189,692 |  |
| Commodity price risk management gain (loss), net   | (47,240 | ) |   | 80,704 |  |
| Other income                                       | 2,615 |  |   | 3,311 |  |
| Total revenues                                     | 260,600 |  |   | 273,707 |  |
| Costs, expenses and other                          |   |   |   |
| Lease operating expenses                           | 29,636 |  |   | 19,789 |  |
| Production taxes                                   | 20,169 |  |   | 12,399 |  |
| Transportation, gathering, and processing expenses | 7,313 |  |   | 5,902 |  |
| Exploration, geologic, and geophysical expense     | 2,646 |  |   | 954 |  |
| Impairment of properties and equipment             | 33,188 |  |   | 2,193 |  |
| General and administrative expense                 | 35,696 |  |   | 26,315 |  |
| Depreciation, depletion, and amortization          | 126,788 |  |   | 109,316 |  |
| Accretion of asset retirement obligations          | 1,288 |  |   | 1,768 |  |
| (Gain) loss on sale of properties and equipment    | 1,432 |  |   | (160 | ) |
| Other expenses                                     | 2,768 |  |   | 3,528 |  |
| Total costs, expenses and other                    | 260,924 |  |   | 182,004 |  |
| Income (loss) from operations                      | (324 | ) |   | 91,703 |  |
| Interest expense                                   | (17,529 | ) |   | (19,467 | ) |
| Interest income                                    | 148 |  |   | 240 |  |
| Income (loss) before income taxes                  | (17,705 | ) |   | 72,476 |  |
| Income tax (expense) benefit                       | 4,566 |  |   | (26,330 | ) |
| Net income (loss)                                  | $ | (13,139 | ) |   | $ | 46,146 |  |
|                                               |   |   |   |
| Earnings per share:                                |   |   |   |
| Basic                                              | $ | (0.20 | ) |   | $ | 0.70 |  |
| Diluted                                            | $ | (0.20 | ) |   | $ | 0.70 |  |
|                                               |   |   |   |
| Weighted-average common shares outstanding:        |   |   |   |
| Basic                                              | 65,957 |  |   | 65,749 |  |
| Diluted                                            | 65,957 |  |   | 66,117 |  |

----

|                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------|
|                                                                                                                                                              |  |  |  |  |  |  |  |  |
|                                                                                                                                                         |   | March 31, 2018 |   | December 31, 2017 |
| Assets                                                                                                                                                       |   |   |   |   |
| Current assets:                                                                                                                                              |   |   |   |   |
| Cash and cash equivalents                                                                                                                                    |   | $ | 45,923 |  |   | $ | 180,675 |  |
| Accounts receivable, net                                                                                                                                     |   | 181,025 |  |   | 197,598 |  |
| Fair value of derivatives                                                                                                                                    |   | 28,610 |  |   | 14,338 |  |
| Prepaid expenses and other current assets                                                                                                                    |   | 8,897 |  |   | 8,613 |  |
| Total current assets                                                                                                                                         |   | 264,455 |  |   | 401,224 |  |
| Properties and equipment, net                                                                                                                                |   | 4,231,257 |  |   | 3,933,467 |  |
| Assets held-for-sale, net                                                                                                                                    |   | 1,647 |  |   | 40,084 |  |
| Other assets                                                                                                                                                 |   | 24,798 |  |   | 45,116 |  |
| Total Assets                                                                                                                                                 |   | $ | 4,522,157 |  |   | $ | 4,419,891 |  |
|                                                                                                                                                         |   |   |   |   |
| Liabilities and Stockholders' Equity                                                                                                                         |   |   |   |   |
| Liabilities                                                                                                                                                  |   |   |   |   |
| Current liabilities:                                                                                                                                         |   |   |   |   |
| Accounts payable                                                                                                                                             |   | $ | 195,703 |  |   | $ | 150,067 |  |
| Production tax liability                                                                                                                                     |   | 36,650 |  |   | 37,654 |  |
| Fair value of derivatives                                                                                                                                    |   | 110,683 |  |   | 79,302 |  |
| Funds held for distribution                                                                                                                                  |   | 97,611 |  |   | 95,811 |  |
| Accrued interest payable                                                                                                                                     |   | 13,760 |  |   | 11,815 |  |
| Other accrued expenses                                                                                                                                       |   | 33,777 |  |   | 42,987 |  |
| Total current liabilities                                                                                                                                    |   | 488,184 |  |   | 417,636 |  |
| Long-term debt                                                                                                                                               |   | 1,154,528 |  |   | 1,151,932 |  |
| Deferred income taxes                                                                                                                                        |   | 187,183 |  |   | 191,992 |  |
| Asset retirement obligations                                                                                                                                 |   | 73,905 |  |   | 71,006 |  |
| Fair value of derivatives                                                                                                                                    |   | 26,426 |  |   | 22,343 |  |
| Other liabilities                                                                                                                                            |   | 94,557 |  |   | 57,333 |  |
| Total liabilities                                                                                                                                            |   | 2,024,783 |  |   | 1,912,242 |  |
|                                                                                                                                                         |   |   |   |   |
| Commitments and contingent liabilities                                                                                                                       |   |   |   |   |
|                                                                                                                                                         |   |   |   |   |
| Stockholders' equity                                                                                                                                         |   |   |   |   |
| Common shares - par value $0.01 per share, 150,000,000 authorized, 65,999,010 and 65,955,080 issued as of March 31, 2018 and December 31, 2017, respectively |   | 660 |  |   | 659 |  |
| Additional paid-in capital                                                                                                                                   |   | 2,504,663 |  |   | 2,503,294 |  |
| Retained earnings (deficit)                                                                                                                                  |   | (6,435 | ) |   | 6,704 |  |
| Treasury shares - at cost, 29,255 and 55,927 as of March 31, 2018 and December 31, 2017, respectively                                                        |   | (1,514 | ) |   | (3,008 | ) |
| Total stockholders' equity                                                                                                                                   |   | 2,497,374 |  |   | 2,507,649 |  |
| Total Liabilities and Stockholders' Equity                                                                                                                   |   | $ | 4,522,157 |  |   | $ | 4,419,891 |  |
|                                                                                                                                                         |   |   |   |   |

----

|                                                                                       |
|---------------------------------------------------------------------------------------|
|                                                                                       |  |  |  |  |  |  |  |  |
|                                                                                  |   | Three Months Ended  March 31, |
|                                                                                  |   | 2018 |   | 2017 |
| Cash flows from operating activities:                                                 |   |   |   |   |
| Net income (loss)                                                                     |   | $ | (13,139 | ) |   | $ | 46,146 |  |
| Adjustments to net income (loss) to reconcile to net cash from operating activities:  |   |   |   |   |
| Net change in fair value of unsettled commodity derivatives                           |   | 21,202 |  |   | (80,153 | ) |
| Depreciation, depletion and amortization                                              |   | 126,788 |  |   | 109,316 |  |
| Impairment of properties and equipment                                                |   | 33,188 |  |   | 2,193 |  |
| Accretion of asset retirement obligations                                             |   | 1,288 |  |   | 1,768 |  |
| Non-cash stock-based compensation                                                     |   | 5,261 |  |   | 4,454 |  |
| (Gain) loss on sale of properties and equipment                                       |   | 1,432 |  |   | (160 | ) |
| Amortization of debt discount and issuance costs                                      |   | 3,246 |  |   | 3,184 |  |
| Deferred income taxes                                                                 |   | (4,809 | ) |   | 26,280 |  |
| Other                                                                                 |   | 515 |  |   | 722 |  |
| Changes in assets and liabilities                                                     |   | 30,177 |  |   | 25,750 |  |
| Net cash from operating activities                                                    |   | 205,149 |  |   | 139,500 |  |
| Cash flows from investing activities:                                                 |   |   |   |   |
| Capital expenditures for development of crude oil and natural gas properties          |   | (196,917 | ) |   | (129,826 | ) |
| Capital expenditures for other properties and equipment                               |   | (1,066 | ) |   | (821 | ) |
| Acquisition of crude oil and natural gas properties, including settlement adjustments |   | (180,825 | ) |   | 6,181 |  |
| Proceeds from sale of properties and equipment                                        |   | 20 |  |   | 737 |  |
| Proceeds from divestiture                                                             |   | 39,023 |  |   | — |  |
| Restricted cash                                                                       |   | 1,249 |  |   | — |  |
| Purchases of short-term investments                                                   |   | — |  |   | (49,890 | ) |
| Net cash from investing activities                                                    |   | (338,516 | ) |   | (173,619 | ) |
| Cash flows from financing activities:                                                 |   |   |   |   |
| Proceeds from revolving credit facility                                               |   | 35,000 |  |   | — |  |
| Repayment of revolving credit facility                                                |   | (35,000 | ) |   | — |  |
| Purchase of treasury stock                                                            |   | (2,255 | ) |   | (2,017 | ) |
| Other                                                                                 |   | (379 | ) |   | (340 | ) |
| Net cash from financing activities                                                    |   | (2,634 | ) |   | (2,357 | ) |
| Net change in cash, cash equivalents, and restricted cash                             |   | (136,001 | ) |   | (36,476 | ) |
| Cash, cash equivalents, and restricted cash, beginning of period                      |   | 189,925 |  |   | 244,100 |  |
| Cash, cash equivalents, and restricted cash, end of period                            |   | $ | 53,924 |  |   | $ | 207,624 |  |

----

----

|         |                                                                                                                                                     |
|---------|-----------------------------------------------------------------------------------------------------------------------------------------------------|
| • | changes in worldwide production volumes and demand, including economic conditions that might impact demand and prices for the products it produces; |

|         |                                                                                                                                                     |
|---------|-----------------------------------------------------------------------------------------------------------------------------------------------------|
| • | volatility of commodity prices for crude oil, natural gas, and natural gas liquids ("NGLs") and the risk of an extended period of depressed prices; |

|         |                                                                       |
|---------|-----------------------------------------------------------------------|
| • | reductions in the borrowing base under its revolving credit facility; |

----

|         |                                                                                                                                                                                                                                                                   |
|---------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| • | impact of governmental policies and/or regulations, including changes in environmental and other laws, the interpretation and enforcement of those laws and regulations, liabilities arising thereunder, and the costs to comply with those laws and regulations; |

|         |                                                                                                            |
|---------|------------------------------------------------------------------------------------------------------------|
| • | declines in the value of its crude oil, natural gas, and NGLs properties resulting in further impairments; |

|         |                                          |
|---------|------------------------------------------|
| • | changes in estimates of proved reserves; |

|         |                                                                |
|---------|----------------------------------------------------------------|
| • | inaccuracy of reserve estimates and expected production rates; |

|         |                                                                                    |
|---------|------------------------------------------------------------------------------------|
| • | potential for production decline rates from its wells being greater than expected; |

|         |                                                                                                 |
|---------|-------------------------------------------------------------------------------------------------|
| • | timing and extent of its success in discovering, acquiring, developing, and producing reserves; |

|         |                                                                                                                                                                                                                                                        |
|---------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| • | availability of sufficient pipeline, gathering, and other transportation facilities and related infrastructure to process and transport its production and the impact of these facilities and regional capacity on the prices received for production; |

|         |                                                     |
|---------|-----------------------------------------------------|
| • | timing and receipt of necessary regulatory permits; |

|         |                                                                                    |
|---------|------------------------------------------------------------------------------------|
| • | risks incidental to the drilling and operation of crude oil and natural gas wells; |

|         |                                                                    |
|---------|--------------------------------------------------------------------|
| • | losses from its gas marketing business exceeding its expectations; |

|         |                                                                                                                                                                           |
|---------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| • | difficulties in integrating its operations as a result of any significant acquisitions, including its pending acquisitions and acreage exchanges in the Wattenberg Field; |

|         |                                                                                                                                                  |
|---------|--------------------------------------------------------------------------------------------------------------------------------------------------|
| • | increases or changes in operating costs, severance and ad valorem taxes, and increases or changes in drilling, completion, and facilities costs; |

|         |                                                                                                                       |
|---------|-----------------------------------------------------------------------------------------------------------------------|
| • | availability of supplies, materials, contractors and services that may delay the drilling or completion of its wells; |

|         |                                                                    |
|---------|--------------------------------------------------------------------|
| • | potential losses in acreage due to lease expirations or otherwise; |

|         |                                                                                                                                        |
|---------|----------------------------------------------------------------------------------------------------------------------------------------|
| • | increases or adverse changes in construction costs and procurement costs associated with future build out of midstream-related assets; |

|         |                                                        |
|---------|--------------------------------------------------------|
| • | future cash flows, liquidity, and financial condition; |

|         |                                              |
|---------|----------------------------------------------|
| • | competition within the oil and gas industry; |

|         |                                   |
|---------|-----------------------------------|
| • | availability and cost of capital; |

|         |                                                        |
|---------|--------------------------------------------------------|
| • | success in marketing crude oil, natural gas, and NGLs; |

|         |                                                             |
|---------|-------------------------------------------------------------|
| • | effect of crude oil and natural gas derivatives activities; |

|         |                                                                                                                                                        |
|---------|--------------------------------------------------------------------------------------------------------------------------------------------------------|
| • | impact of environmental events, governmental and other third-party responses to such events, and its ability to insure adequately against such events; |

|         |                                       |
|---------|---------------------------------------|
| • | cost of pending or future litigation; |

|         |                                                                         |
|---------|-------------------------------------------------------------------------|
| • | effect that acquisitions it may pursue has on its capital requirements; |

|         |                                                                                     |
|---------|-------------------------------------------------------------------------------------|
| • | its ability to retain or attract senior management and key technical employees; and |

|         |                                                                                     |
|---------|-------------------------------------------------------------------------------------|
| • | success of strategic plans, expectations, and objectives for its future operations. |

----