Hybrid auto sales have been smoking this month as consumers look for ways to cut the cost of driving.

The market share of hybrid model sales has jumped an estimated 5 percentage points to 18% of new-vehicle retail sales, according to a JD Power-GlobalData August forecast. That’s up a dramatic 36% year-over-year as consumers face high gas prices.

The segment results would have been even stronger if not for what the market watcher called “unusually low availability” of many popular hybrids.

Still, a greater abundance of hybrid models on the market now is boosting their sales, JD Power said.

Overall retail auto sales have proved healthy this month at 1.1 million units despite high prices and monthly payments. Year-over-year, deliveries are estimated to drop about 7%, but that’s largely due to last year’s electric-vehicle sales surge ahead of the elimination of federal purchase tax credits.

JD Power forecasts the seasonally adjusted annual rate at 13 million units, down about 400,000 year-over-year.

Consumers got a little break on auto loans this month with a projected average interest rate drop of six basis points to about 6.6%, the lowest for the month of August in four years.

Still, that’s “not enough to offset the structural affordability pressures on buyers,” JD Power President of OEM Solutions Thomas King said.

Average monthly payments are forecast to be up about 4% to $812, the highest on record for an August as low trade-in equity dings buyers. About 29% of trade-ins this month have carried negative equity, JD Power data show.

LEARN MORE: California Hybrids Reach State Record