SOUTH PORTLAND — South Portland-based Wright Express Corp. reported revenue of $120.1 million in the first quarter of 2011, a 43 percent jump over the $83.8 million the company earned during the same period last year.

Net income for the period, based on generally accepted accounting principles, dropped to $12.1 million from $18.6 million.

However, the company’s adjusted net income grew 23 percent to $29.2 million, or 75 cents per diluted share, during the period.

CEO Michael Dubyak said adjusted net income better represents Wright’s performance because it eliminates volatility associated with the company’s extensive fuel price hedges. He added that financial analysts, when evaluating the company, focus entirely on adjusted net income.

Dubyak attributed the gains to a number of factors, including momentum in the company’s payment processing business.

During the first quarter, Wright Express processed 6 percent more domestic fuel-purchase transactions, the largest gain since before the recession.

Dubyak said those gains indicate “the economy is gaining some momentum.”

Total fuel purchase transactions, including overseas transactions, grew 14 percent during the period, gains that include business from the company’s recently acquired Australian operation.

Wright Express serviced 5.4 million vehicles in the first quarter, up 21 percent from the same period last year.

The company also reported strong results in its corporate MasterCard division. The company’s card holders used their cards to purchase $1.4 billion in goods and services, up 68 percent from the first quarter of 2010. MasterCard revenue jumped 80 percent during the period.

Based on strong first-quarter results, Wright upped its full-year 2011 guidance. The company now expects to earn between $533 million and $553 million in revenue in the year.

“We believe our transactions for North America will continue to be strong and we see international (business) continuing to be a big part of our story,” said Dubyak. “We feel very comfortable that we will do better than we initially (thought).”

Wright Express’ primary business is processing gasoline and diesel fuel purchase transactions for commercial fleets in the United States and abroad.