WASHINGTON (AP) — The United States is still growing older, but the trend is reversing itself in the Great Plains, thanks to a liberal application of oil.

Census Bureau data released Thursday shows the median age in the U.S. went up a little bit last year, from 37.5 years to 37.6 years.

When the data is broken down by state, seven states actually got younger — Alaska, Hawaii, Montana, North Dakota, Oklahoma, South Dakota and Wyoming.

The census Bureau says that the five mainland states are in the middle of the country's oil and gas boom and are attracting young men looking for work.

The largest decline in age — 1.6 years — is in the town of Williams, North Dakota. It's the center of the country's Bakken shale energy boom.