Monthly bills for most South Jersey residential electric customers will go up slightly on June 1, but the results of the state’s annual power supply auction suggest that bigger increases may be in the offing in following years.

The New Jersey Board of Public Utilities on Thursday approved the results of its annual electricity auction, which sets the price of basic generation service for the next year.

The monthly bill for Public Service Electric & Gas Co. residential customers will increase 0.3 percent, or about 35 cents for a customer using 650 kilowatts per month; bills for Atlantic City Electric residential customers will increase 0.8 percent, or about 90 cents for 650 kilowatts of usage. Jersey Central Power and Light Co. residential bills will decrease 2.2 percent, or about $2.03 per month.

The annual competitive auctions are for three-year contracts and determine the price for about one-third of the utilities’ supply. This year’s winning contracts will replace contracts from three years ago. But the winning prices are between 2.4 percent and 7.6 percent greater than the prices fetched in last year’s auction, which suggests an upward trend that will translate to higher bills in the future when the cheaper contracts expire.

The BPU says the auction results do not predict a future increase.