The 2012 NCAA Division I Men’s Basketball Championship through Saturday’s contests garnered the highest ratings for March Madness in 18 years, according to Multichannel News. The series has averaged a 5.3 household rating across TBS, CBS, TNT and TruTV through March 17 — up 4% from a 5.1 in 2011 and a 15% bump over over a 4.6 rating in 2010, according to Nielsen fast nationals. Games averaged 8 million viewers, up 3% from last year’s 7.8 million viewers at the same time in the tournament and 14% ahead of the 7 million viewers during the comparable 2010 period. St. Patrick’s Day delivered a surge in viewership giving the four networks the highest-rated and most watched Saturday since 2007. Saturday’s game ratings averaged a 6.1, 3% over last year’s 5.9 and 13% above the 5.4 mark in 2010. The 9.3 million viewer average matched last year and was 11% more than the 8.4 million viewers in 2010. Friday’s games generated record numbers for the four networks with a 5.4 household rating and 8 million viewers — the most-watched Friday since the event expanded to four telecast windows in 1991. Those deliveries were up 8% compared with a 5.0 rating in 2011 and 29% versus 2010′s 4.2 rating. Turner and CBS are in the second of a 14-year, $10.8 billion deal whereby the four networks air each of the tourney’s 67 games in a national window. Coverage previously was regionalized on CBS.