Marathon Petroleum Corp. revenues have climbed again, thanks in large part to the growth of Speedway, a top 10 employer in Clark County.

Speedway’s operating income jumped 30 percent over last year to $107 million as it sold more gasoline, marking the second quarter of growth this year.

“Speedway is a key piece of Marathon’s asset base, which has grown through a number of acquisitions,” Marathon spokesman Shane Pochard said.

The company currently employs about 700 people at its Enon headquarters in Clark County and has 1,455 stores across the nation.

Speedway, one of Marathon’s main subsidiaries, sold 756 million gallons of gasoline for the three months ending June 30, compared to 725 million in second quarter 2011, according to a quarterly finance report released Tuesday.

The company also earned $776 million in Speedway merchandise sales, up from $743 million in same time last year.

In one month, Speedway acquired 97 locations in the Ohio, Kentucky and Indiana — ending with the acquisition of 10 Road Ranger gas stations in Ohio and Northern Kentucky in July.

“Obviously gas and diesel sales, as well as merchandise sales, are the major revenue streams,” Pochard added.

The amount of gas sold at Speedway is up, which might be the result of an increase in locations or lower gas prices, according to a national petroleum expert.

“Demand for gas is generally lower but Speedway tends to be a very competitive chain of stations,” said Patrick DeHaan, senior petroleum analyst for Gasbuddy.com. He said Speedway’s loyalty program is one of the best in the country and could attract many customers.

Gas sales “could be higher because of the number of stations, they had several acquisitions of smaller competition in their region,” DeHaan said.

He also said that while current gas prices are almost identical to a year ago, about a month ago there was a drop in prices that could have lead to an increase of sales.

Besides Speedway gas and merchandise sales, other Marathon subsidiaries saw growth as well. The revenue from refining and marketing operations increased this quarter.

According to Marathon’s second quarter results released Tuesday, the company’s net income is $814 million — or $2.38 per diluted share — for three months ending on June 30.

In the second quarter of 2011, the company’s net income was $802 million or $2.24 per diluted share.

Speedway has also earned major accolades from a national survey. Speedway was ranked as the top convenience store brand by Harris Interactive, a market research firm that surveyed more than 25,000 consumers about a number of industries.

Harris officials were unavailable for comment.