SOUTH PORTLAND — South Portland-based Wright Express reported net income of $48.1 million or $1.23 per diluted share in the third quarter of 2011, up from $20.6 million or 53 cents per share in the third quarter of 2010, the company announced today.

Revenue during the three-month period, which ended Sept. 30, increased 52 percent to $151.9 million.

Wright Express, which processes automotive fuel purchases for commercial fleets and other credit card transactions, provided services to an average of 6.5 million vehicles worldwide in the third quarter, up 29 percent, according to a press release. The number of fuel transactions processed jumped 19 percent during the period to $85.1 million, and corporate card purchase volume increased 83 percent to $2.4 billion.

CEO Michael Dubyak said the best indication of the company’s financial health is adjusted net income, which reflects the company’s extensive fuel hedges.

During the third quarter, adjusted net income increased 38 percent to $38.7 million, up from $28.1 million during the period last year.

Dubyak said the results show that the company continues to grow its core fuel-purchase business despite a sluggish, but stable, economy.

He added that the results show expansion of the company’s corporate credit cards, which are used by travel agencies like Priceline to pay hotel and car rental partners. He said Wright Express expects to expand its card business into Europe in the first half of 2012.

In the media release, Dubyak said Wright Express has diversified in recent years into new businesses, which have provided a foundation for growth.

“Even in the current environment, Wright Express is well positioned to deliver continued strong performance. Looking ahead, we are confident that the positive momentum in our business will continue as our more recent initiatives gain traction and we capitalize on the many opportunities in front of us, including new customer wins and multi-faceted expansion of the business,” he said.

Wright Express has some 850 employees, including more than 500 in Maine. 

The company’s stock traded at $48.12 on the New York Stock Exchange this morning, up from $44.72 Tuesday.