The trade deficit in the United States widened more than expected in September, to $36.5 billion, in part because of an increase in oil prices, the Commerce Department said Friday.

The department's data showed an 18.2 percent increase in the difference of the value of imports and exports, known as the trade balance.

Both imports and exports rose, but an increase in the price of oil, which climbed $3.42 to $68.17 a barrel in September, helped widen the gap. The United States imported $19.51 billion in oil in September, up from $17.38 billion in August.

Overall, imports rose 5.8 percent in September to $168.4 billion from $159.1 billion, and exports grew at half that pace — 2.9 percent — to $132 billion from $128.3 billion.

Friday's data suggested the demand for American products abroad was starting to recover, helped by a weak dollar. After holding up for much of 2008, exports fell off late in the year as other countries began to struggle. They have recovered since, and September's exports returned to December 2008 levels.

Strong export growth and a revival in consumer spending are considered a key to a recovery in the United States. As of September, the trade deficit is running at an annual rate of $366 billion, about half of last year's $695.9 billion. The deficit with China, which had been easing, rose 9.2 percent to $22.1 billion last month, its highest level in 10 months.

While the economy remains weak, Nariman Behravesh, chief economist at IHS Global Insight in Lexington, Mass., said the rise in imports might indicate manufacturers in the United States were building inventories — a carmaker importing Japanese auto parts, for instance — in anticipation of higher demand from American consumers.

"It's a very strong signal that the domestic economy is recovering," he said.

Behravesh said he expected the appetite for imported goods to remain low as consumers try to rein in spending.

Analysts, however, expect American companies will benefit from the weak dollar.