The company reported adjusted earnings of $15.5 million, or 67 cents per share. Analysts' average estimate was 62 cents per share, according to Thomson Reuters.
Group 1 posted adjusted earnings of $10.4 million, or 44 cents per share, during the same quarter last year. Total revenue rose 18.3 percent to $1.4 billion, primarily driven by sales of new vehicles.
The company also raised the possibility that deliveries of vehicles from Japanese automakers could drop as much as 50 percent this summer, due to disruptions in the global supply chain after the March 11 earthquake in northern Japan.
"If deliveries are reduced to the extent mentioned above, it is likely that inventory levels will constrain sales for the second quarter and possibly third quarter," the company said in a statement.
For showrooms that could get fewer vehicles, Group 1 will cut advertising spending and other expenses. It expects higher new vehicle margins in coming months for those stores.
The company said over the coming months it will focus on sales of used vehicles and its parts-and-service businesses, which account for more than 65 percent of gross profit.
Group 1, based in Houston, ranks No. 4 on the Automotive News list of the top 125 dealership groups in the United States with new vehicle sales of 97,511 in 2010.