State of Oklahoma provides a credit of 50% of the cost of PHEV Conversion

Alternative Fuel Vehicle (AFV) Tax Credit For tax years beginning before January 1, 2015, a one-time income tax credit is available for 50% of the incremental cost of purchasing a new original equipment manufacturer AFV or converting a vehicle to operate on an alternative fuel. The state also provides a tax credit for 10% of the total vehicle cost, up to $1,500, if the incremental cost of a new AFV cannot be determined or when an AFV is resold, as long as a tax credit has not been previously taken on the vehicle. Equipment used for conversions must be new and must not have been previously used to modify or retrofit any vehicle. The alternative fuels eligible for the credit are compressed natural gas, liquefied natural gas, liquefied petroleum gas, hydrogen fuel cell, and electricity. Hydrogen fuel cell vehicles are eligible through December 31, 2010, and only qualified electric vehicles placed into service before July 1, 2010, are eligible. For vehicles propelled by electricity only, the credit is based on the full purchase price of the vehicle. For vehicles equipped with an internal combustion engine and powered partially by electricity, such as a hybrid electric vehicle, the credit is based on the cost of the portion of the motor vehicle attributable to the propulsion of the vehicle by electricity. Tax credits may be carried forward for up to five years. (Reference House Bill 3024, 2010, and Oklahoma Statutes 68-2357.22)