Consumers are dining out more frequently now due to lower gas prices, higher household incomes and increased confidence.

WASHINGTON — For the first time on record, monthly sales at restaurants surpassed grocery store sales, according to the National Restaurant Association. Lower gas prices, higher household incomes and increased confidence are motivating consumers to dine out more frequently, said Bruce Grindy, chief economist for the N.R.A.

The gap between grocery store sales and restaurant sales began narrowing in 2010, as more consumers began purchasing groceries at alternative retail formats. December 2014 marked the first month on record that restaurant sales exceeded grocery store sales, and the trend has accelerated in the months since. In June 2014, grocery store sales exceeded restaurant sales by $1.6 billion, and in April 2015, restaurant sales surpassed grocery store sales by $1.5 billion.

Restaurants are most likely benefiting from lower gas prices, Mr. Grindy said. In a survey commissioned by the N.R.A. and conducted by ORC International of 1,008 adults between April 30 and May 3, 80% of car owners said the recent decline in gas prices had a positive impact on household finances, and 49% reported the fuel savings increased their willingness and ability to buy meals, snacks or beverages from restaurants, fast-food outlets and coffee shops. The figure skews higher for individuals in lower-income houses, Mr. Grindy said.

Overall, a third of respondents said they are dining out in restaurants more often than in the year before, citing reasons that included increased confidence in their financial situation (63%), lower gas prices (56%), higher household incomes (46%) and a new job (30%).

“With gas prices likely contributing to the dramatic shift in consumer spending during the last several months, the question is if these spending patterns will hold when gas prices increase again,” Mr. Grindy said. “To be sure, there appears to be even more room for growth in the months ahead. When asked about their current restaurant usage, a significant proportion of the American public say they would like to be patronizing restaurants more often.”

Nearly two in five consumers said they are not dining in restaurants (38%) or purchasing food for takeout or delivery (37%) as often as they would like.

“Putting these results in a historical context, this measure of pent-up demand remains well above pre-recession levels,” Mr. Grindy noted. “On a consistent basis during the stronger restaurant business environment of the mid-2000s, typically only one-quarter of adults said they were not patronizing restaurants as frequently as they would like.”