Hawai'i gasoline prices, which fell by about 50 cents this week, are likely to decline another 6 cents next week as the state's new price cap law is adjusted to reflect falling costs on the Mainland.

However, the trend toward lower prices could end the following week — beginning Oct. 3 — if Hurricane Rita disrupts supplies and forces Mainland prices higher.

Hawai'i became the only state in the nation to cap wholesale gasoline prices on Sept. 1. The price cap formula is adjusted weekly based on wholesale prices in Los Angeles, the Gulf Coast and New York.

Because prices in those markets were lower in the past week, Hawai'i's gas cap will fall when the state announces today what the cap will be starting Monday.

According to Advertiser calculations, the state's wholesale gasoline price ceiling for regular on O'ahu will drop by about 6 cents to $2.92, including taxes. When dealer mark-up is added, most Honolulu drivers will likely be paying between $3.05 and $3.15 a gallon for regular next week.

The wholesale price caps are set every Wednesday based on Mainland prices during the preceding five business days. The wholesale cap is an average of those prices plus a margin to account for the costs of shipping, distributing and marketing gasoline in Hawai'i.

Next week's drop could have been greater if not for a jump in Mainland wholesale prices on Monday amid concerns about Hurricane Rita's impact on oil prices.

Forecasters said Rita, a category 3 hurricane, could build in intensity as it crosses the Gulf of Mexico and is likely to hit Texas over the weekend. Texas has more than a quarter of the U.S. total refining capacity, according to the U.S. Department of Energy.

Hawai'i prices spiked sharply last week in response to a rise in Mainland prices caused by supply disruptions from Hurricane Katrina, which ripped into the Gulf Coast Aug. 29.

Reach Sean Hao at shao@honoluluadvertiser.com.