Turning to Slide 4 of our presentation for an overview of Level 3 standalone fourth quarter results, we ended the year on a strong note. Please keep in mind that all -- in all of the results in my discussion here exclude the effects of intercompany eliminations and purchase price -- purchase accounting adjustments with Global Crossing and acquisition-related costs.
Core Network Services revenue grew by 2.6% sequentially and 7.9% year-over-year on a constant currency basis. Adjusted EBITDA increased sequentially and 15% year-over-year. We had a great quarter for free cash flow, generating $103 million of positive free cash flow.
For Global Crossing, on a constant currency basis, Invest and Grow revenues declined 1% sequentially and increased 3% year-over-year. Sequential declines were a result of expected declines in U.K. government revenues. Excluding U.K. government revenues, Invest and Grow revenues were roughly flat sequentially. Invest and Grow revenues for GC Impsat grew 2% sequentially with particular strength from enterprise customers.
We continued to improve our maturity profile and liquidity position through transactions during the quarter and earlier this year.Turning to the detailed results for the fourth quarter on Slide 5. Level 3, on a standalone basis, saw a sequential and year-over-year growth in Core Network Services revenue across all of our customer channels. Our CDN revenue grew 14% sequentially compared to 9% in the prior quarter. Compared to the fourth quarter in 2010, CDN revenue grew 91%. With our larger revenue base, CDN services revenue now represent 1.6% of our CNS revenue. Also, Voice Services revenue was $144 million this quarter compared to $152 million in the third quarter. As we are continuing to manage our combined Wholesale Voice platform for margin growth, we expect continued volatility in Wholesale Voice Services revenue going forward. Read the rest of this transcript for free on seekingalpha.com