Even though most states stipulate that consumers be 18 years old to buy tobacco products, a new study finds that clerks who work in convenience stores that sell gasoline are the most likely to sell tobacco to minors.

When compared to other retailers such as restaurants, bars and tobacco discount stores, gas-convenience stores sold the most tobacco products during random checks, according to the study appearing in the August issue of the American Journal of Preventive Medicine.

To cut down smoking among young people, most states use “youth operatives” to measure compliance with state age requirements. The researchers analyzed data from 8,879 such compliance checks done throughout King County in Washington State between January 2001 and March 2005. Ninety-one youth operatives, ages 14 to 17, conducted the checks.

By checking whether “a sale was made” to a minor, the study found overall underage tobacco sales were 7.7% for the study period. Convenience stores selling gas had 9.3% of sales, compared with 3.4% for tobacco stores, 5.2% for restaurants and 7.4% for grocery stores.

Lead author Dave Pearson, of the Group Health Community Foundation in Seattle, said there might be something about gas stations that results in lack of attention to the age requirements. It could be the combination of customers wanting to get in and out fast and clerks being required to multi-task; for example, watching the counter and gas pumps while making financial transactions.

The authors also found that clerks under 18 had “very high” sales to minors, as did female clerks. However, sales to minors dropped when the clerk asked for ID or age of the buyer.