Hawai'i gasoline prices, hovering around an almost four-month low, may dip slightly next week in line with Mainland prices.

Gasoline prices could decline by 1 cent or more next week under the state's gas cap law, Advertiser calculations show. The Hawai'i Public Utilities Commission is scheduled to announce today a new cap that will take effect Monday.

Hawai'i's wholesale price cap, the only one in the nation, has been cut for seven consecutive weeks. Retail prices, which aren't regulated by the law, may not be falling as fast as they are nationally, American Automobile Association data shows.

The national average for a gallon of regular was $2.148 on Monday night, or about 30 percent lower than a high of $3.057 a gallon reached in September.

Hawai'i's average was $2.679, or 27.3 percent less than the zenith of $3.684, also reached in September.

Wholesale gasoline prices declined on the Mainland in the past two days on speculation that fuel inventories are sufficient to meet demand. The cap is based on five days of wholesale prices in New York, the Gulf Coast and Los Angeles.

The Advertiser's estimate of next week's cap is based on data from Bloomberg News. The projection can vary by a few cents from the official state price, which is computed using figures supplied by Oil Price Information Service.

The state's diesel fuel prices are the highest nationally at $3.341 a gallon. The U.S. average is 2.61 a gallon. Diesel wholesale prices are not covered under the state's wholesale price cap.

Reach Greg Wiles at gwiles@honoluluadvertiser.com.