Higher prices for imported oil have pushed the U.S. trade deficit to its highest level in three years.

The U.S. Commerce Department said Tuesday the official trade gap hit $50.2 billion in May, a 15 percent increase over the previous month.

The report cited the high cost of imported oil as the main factor. Oil prices averaged almost $109 a barrel in May, pushing the country’s petroleum trade deficit to more than $30 billion.

The trade deficit – the difference between the value of the goods and services a country sends abroad and what it brings in – is a key measure of economic health. And the report does show some encouraging signs for the U.S. economy.

Imports rose 2.6 percent in May, reflecting higher demand for industrial supplies, automotive parts and food and beverages.

Exports also had a strong performance but slipped slightly from a record high in April due to a decrease in foreign demand for industrial supplies.

The U.S. trade deficit with China widened in May to $25 billion.

U.S. lawmakers and the Obama administration have been critical of Beijing for keeping China’s currency artificially weak, making Chinese exports relatively cheap and driving up China’s trade surplus with the United States. They have repeatedly called on China to allow the yuan to strengthen more quickly to reduce that imbalance.