While there have been few polls in Puerto Rico, the general consensus is that Clinton is favored to win this common wealth territory with a substantial margin. Of course, Clinton is unlikely to catch up with Obama on delegates despite that. There is also a real chance that enough super delegates will move to Barack Obama’s camp in the next few weeks that the Puerto Rico primary will no longer matter.
However, the Puerto Rico primary might still determine the winner of total popular votes. On May 20th, Hillary Clinton picked up about 250,000 more votes than Obama in Kentucky, but lost by about 100,000 votes in Oregon. This means that she is only about 150,000 votes behind Obama in the total number of votes casted during the primary season (counting Florida but not Michigan, where Obama was not on the ballot). A double digit victory in Puerto Rico is very likely to close that gap for her. If Clinton can end the nomination battle as the winner of popular votes, it would greatly improve her chance of stopping Obama from becoming the nominee.