The 33-year-old Bryans' first-round win at the Valencia Open on Wednesday means they cannot be overtaken by No. 2-ranked pair Michael Llodra and Nenad Zimonjic.
Since 2003, the Bryans have only twice failed to finish No 1 - in 2004 and 2008. This year, they have won seven titles, including the Australian Open and Wimbledon. They've won an Open-era record 74 titles.
The twins have been ranked No 1 in the individual doubles rankings for 265 weeks and will overtake John McEnroe's record of 270 on December 12.
Bob said of McEnroe that "he's such a legend and to achieve something like this won't truly set in for a while."