Amoco Corp., long one of the dominant gasoline marketers in the United States, announced plans to form a joint venture intended to give Mexican motorists the convenience of one-stop shopping at Mexican service stations.

Though the idea of convenience stores at gasoline stations is not new in Mexico, it is not widespread, said Jorge Pinon, director general of Amoco Oil de Mexico, the Mexico operating company of Amoco."That's why we are looking at this," Mr. Pinon said in a phone interview

from Mexico. "All of the things the U.S. has taken for granted for the last 10 or 15 years, we will bring that type of operation here."

The one-stop service centers will offer gasoline, car washes, quick oil changes, fast-food and other services under the name Oxxo Express.

The venture is the third foreign marketing project Amoco has announced since early June. The Chicago-based company has said it will spend $60 million to build a service station network in Romania and $150 million to build 150 outlets in Poland.

Amoco is pooling its experience in operating more than 2,800 service station/convenience stores in the United States with Fomento Economico Mexicano SA, a Monterrey-based beverage company with 700 stores in Mexico.

Together, Mr. Pinon said, the companies expect to invest more than $250 million during the next 10 years to build up to 300 stores at existing or new gasoline stations owned and operated by independent dealers with Pemex gasoline franchises.

The dealers "will enter into some sort of commercial relationship with our joint venture to build and/or operate these facilities," Mr. Pinon said.

Petroleos Mexicanos is Mexico's state-owned oil company, which has a monopoly on gasoline sales in Mexico. Pemex dealers want to increase their profitability through the new venture, Mr. Pinon said.

Mexico lacks such comforts as truck stops or roadside inns, he added. The joint venture does not signal a relaxation of Pemex's monopoly, said Mr. Pinon, but he credits the North American Free Trade Agreement, lifting trade

barriers between the United States, Canada and Mexico, with helping the venture.

"We could have gone into this business five or six years ago," Mr. Pinon said. "Nafta was the catalyst for a lot of multinationals. It provided the momentum for us to say there is opportunity here."

Amoco does not sell gasoline in Mexico, but it does market lubricants and compressed natural gas at convenience stores. Also active there are 7-Eleven and Circle K convenience stores.

Mr. Pinon said the new Oxxo Express stores probably will focus on some of Mexico's most heavily populated areas such as Mexico City, Guadalajara and Monterrey.