The average weekly rate for a compact car rental at an airport jumped 51 percent from 2008 levels, to $335.05 in 2009, according to new research as reported by Abrams Consulting Group to the Phoenix Business Journal.

According to the research by the Purchase, N.Y.-based car rental consulting firm, the rate increase occurred as most travel-related costs decreased in 2009.

Rates will continue to increase this year, according to the firm’s president, Neil Abrams. Rental companies’ significant fleet reduction gave them leverage to raise prices, he added.

While fleet sizes fell 25 percent on average across the industry in 2009, and they are down about 50 percent compared with several years ago, demand last year fell by only about 20 percent across the industry. That allowed rental-car companies to raise prices. Rental-car companies are expected to increase fleet sizes gradually as demand increases this year.