With five weeks until the November elections, there is no doubt that Republicans are the heavy favorite to retain control of the U.S. House. The only question is whether they can expand their advantage in a small number of races that could go either way on Election Day.

Currently, Republicans enjoy an advantage in the House of 233 to 199 seats; of the three vacant seats, two trend to the Democrats and one to the GOP.

The various experts who track all 435 House races all agree on the same basic overview, which is that there are more Democratic seats in the "toss up" category than seats held by Republicans.

But, the number of seats in play is very small in percentage terms - maybe just four percent - or less - of House seats are truly up for grabs.

+ Political handicapper Charlie Cook sees 11 Democratic seats in the "toss up" category, to 4 for the Republicans.

+ Larry Sabato at the University of Virginia sees 10 Democratic toss ups to just 3 for the GOP.

+ Stu Rothenberg has 7 Democratic seats as a toss up to just 2 for Republicans.

It's not hard to see the evidence from those four examples - more Democratic seats seem to be on the edge in November than seats held by the GOP.

Republicans are hoping to win back some of the seats they lost in the 2012 elections, and push the GOP majority into historic territory.

After the 242 seats the GOP won in 2010, Republicans have not been above 246 House seats since 1946. The GOP had 247 in 1924, and a high water mark of 302 seats after the 1920 elections.

Here is how the last six elections have gone for the U.S. House:

2012 - Dems +8; 234 Republicans, 201 Democrats

2010 - GOP + 63; 242 Republicans, 193 Democrats

2008 - Dems +21; 257 Democrats, 178 Republicans

2006 - Dems +31; 233 Democrats, 202 Republicans

2004 - GOP +3; 232 Republicans, 202 Democrats

2002 - GOP +8; 229 Republicans, 204 Democrats