Sunoco Marketing said it will impose no processing fees on gasoline and motor oil credit card sales at its service stations.

The Sun Co. unit's move bucks the industry trend toward charging credit customers for the privilage, thereby offering discounts for cash purchases.

"By not charging a fee on gasoline, diesel fuel and motor oil credit sales, we hope our dealers and jobbers will not feel it necessary to charge a higher price on credit card sales as do some of their competitors," said said Edward J. Meyer, general manager of marketing for Sunoco.

He also said that Sunoco and DX dealers also will accept other major oil company credit cards for gasoline purchases of up to $30 beginning Oct. 24 and continuing through the end of the year. Shell Oil took a similar step last month, and other companies have taken other approaches to try to increase their shares of the dwindling gasoline markets.

Although Sun will not charge fees for using oil company cards to buy gasoline, diesel and motor oil, it will charge for using the cards for other purchases and will impose on its dealers a handling charge of between 2.6 and 3 percent on bank and entertainment credit cards.

Sun has more than 3 million credit card accounts and sells approximately one-third of its gasoline marketed through branded dealers on credit cards.