The U.S. added over 300,000 new clean diesel vehicles in 2015 with the state of California leading the way with a 15.4% increase in the number of registered diesel cars and SUVs in 2015, according to a Diesel Technology Forum analysis of the latest Vehicles in Operation (VIO) data.

The analysis, which was compiled by IHS Automotive, is based on 2015 data of VIOs in the U.S. through the end of 2015, according to Diesel Technology Forum.

The analysis reviewed VIO data for passenger vehicles defined as cars, SUVs, full-size pickup trucks, and vans. The Diesel Technology Forum used the data to calculate the top states in registrations and the percentages of diesel and hybrid registrations in each state. The analysis compared 2015 to 2014 data.

“We anticipate the clean diesel car market will stabilize and regain the momentum it had achieved earlier as a variety of new clean diesels are introduced in the U.S. in the very near future,” said Allen Schaeffer, the executive director of the Diesel Technology Forum.

Meanwhile, Texas was No.1 in the nation in total number of registered diesel vehicles ahead of California, Florida, Washington and Pennsylvania

The number of diesel car, SUV, full-size pickup trucks and vans in operation reached 7.7 million in 2015 — an increase of 329,700 over 2014. Hybrid vehicles jumped 331,700 to a total of 3.6 million during the same period.

California and Massachusetts are the only two states that have more hybrid vehicle registrations than diesels, according to the analysis.

California Tennessee, Idaho, and Nevada led the nation with the fast growing registrations for clean diesel cars and SUVs based on their growth within vehicles in operation when data compared to 2014 and 2013, according to the analysis.

Eastern states led the nation in fastest growth of diesel pickup trucks led by Maine, South Carolina, and Florida. Seven of the top 10 states on this list were in the East.

Overall, Texas has the most diesel pickups registered followed by California, Florida, Washington, and Colorado.