U.S. e-commerce sales totaled $194.3 billion in 2011, up 16.1% from $167.3 billion in 2010, according to an estimate released today by the U.S. Commerce Department.

The estimate, not adjusted for seasonality, show that e-commerce is taking a bigger portion of overall retail sales in the United States. 4.6% of total retail spending took place online during 2011, up from 4.3% in 2010, according to the Commerce Department. When excluding sales in categories not commonly bought online—automobiles, fuel, grocery and foodservice sales—Internet Retailer calculates that e-commerce accounted for 8.6% of total retail sales during the year, up from 7.6% in 2010. Total retail sales, which includes e-commerce sales, increased 7.9% in 2011 and totaled $4.2 trillion, according to the Commerce Department.

Seasonally adjusted, 2011 e-commerce sales were $193.4 billion and represented 4.6% of total retail spending.

E-commerce’s strong fourth quarter helped drive this growth. Seasonally adjusted e-retail sales for the fourth quarter of 2011 totaled $51.4 billion, up 15.5% from $44.5 billion a year ago, the Commerce Department reports. In contrast, total retail sales increased 6.8% from the fourth quarter of 2010. E-commerce represented 4.8% of all retail spending during the fourth quarter of 2011, up from 4.4% a year ago.

Without the seasonal adjustment, e-retail sales in the fourth quarter of 2011 totaled $61.8 billion, up 16.1% from $53.2 billion a year ago. E-commerce represented 5.5% of total non-adjusted retail sales during the quarter. When excluding sales in categories not commonly bought online, Internet Retailer calculates that e-commerce accounted for 9.7% of non-adjusted total retail sales during the quarter, up from 8.5% in 2010.

The full-year and quarterly estimates from the Commerce Department are higher than those released earlier this month by comScore Inc. The web measurement firm reported total e-commerce sales increased 13% during 2011 to reach $161.5 billion, and 14% during the fourth quarter to reach $49.7 billion. ComScore draws on online purchase data from its panel of about 1 million U.S. online shoppers. Commerce Department estimates are based on a quarterly survey of more than 11,000 U.S. merchants.