**PUBLIC      SERVICE COMPANY OF OKLAHOMA**

**Computation      of Ratios of Earnings to Fixed Charges **

**(in      thousands except ratio data)**

|                                                                                                                 |   | **Year                  Ended December                  31,**          |    |
|----------------------------------------------------------------------------------------------------------------------|--------|---------------------------------------------------------------------------------------------------------------------|---------|
|                                                                                                                 |   | **2002**                                                                                                       |    | **2003**  |   | **2004** |   | **2005**  |   | **2006**  |   |
| **EARNINGS**                                                                                                         |   |                                                                                                      |    |     |   |     |   |     |   |     |   |
| Income                  Before Income Taxes                                                                          |   | $                                                                                                                   | 63,443  |   | $ | 91,728 |   | $ | 45,351 |   | $ | 88,378 |   | $ | 52,847 |   |
| Fixed                  Charges (as below)                                                                            |   |                                                                                                                | 42,377  |   |   | 46,787 |   |   | 39,475 |   |   | 36,762 |   |   | 44,769 |   |
| **Total                  Earnings**                                                                                  |   | $                                                                                                                   | 105,820 |   | $ | 138,515 |   | $ | 84,826 |   | $ | 125,140 |   | $ | 97,616 |   |
|                                                                                                                 |   |                                                                                                                |    |   |   |   |   |   |   |   |   |   |   |   |   |   |
| **FIXED                  CHARGES**                                                                                   |   |                                                                                                                |    |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Interest                  Expense                                                                                    |   | $                                                                                                                   | 40,422  |   | $ | 44,784 |   | $ | 37,957 |   | $ | 34,094 |   | $ | 40,778 |   |
| Credit                  for Allowance for Borrowed Funds Used                     During Construction |   |                                                                                                                | 673     |   |   | 451 |   |   | 280 |   |   | 668 |   |   | 1,491 |   |
| Trust                  Dividends                                                                                     |   |                                                                                                                | (186    | )  |   | (93 | ) |   | (62 | ) |   | - |   |   | - |   |
| Estimated                  Interest Element in Lease Rentals                                                         |   |                                                                                                                | 1,468   |   |   | 1,645 |   |   | 1,300 |   |   | 2,000 |   |   | 2,500 |   |
| **Total                  Fixed Charges**                                                                             |   | $                                                                                                                   | 42,377  |   | $ | 46,787 |   | $ | 39,475 |   | $ | 36,762 |   | $ | 44,769 |   |
|                                                                                                                 |   |                                                                                                                |    |   |   |   |   |   |   |   |   |   |   |   |   |   |
| **Ratio                  of Earnings to Fixed Charges**                                                              |   |                                                                                                                | 2.49    |   |   | 2.96 |   |   | 2.14 |   |   | 3.40 |   |   | 2.18 |   |