Puerto Rico has 55 delegates in play on June 1.

According to various sources at DemConWatch, Obama's lead over Clinton in pledged delegates is anywhere form 163 to 168.

Assuming an apportionment of delegates that parallels popular vote (more on that below), here is her net delegate gain if she maintains the following percentages in the remaining contests:

Clinton 50% Obama 50% net gain 0
Clinton 55% Obama 45% net gain +56
Clinton 60% Obama 40% net gain +114
Clinton 65% Obama 35% net gain +170

It is only by achieving 65% or more in all the remaining contests that Clinton has a chance of bypassing Obama in his current lead of @165 pledged delegates.

Now the above is assuming that the primaries will end up apportioning delegates according to popular vote. Because of the quirky little laws each state has for apportionment, it ain't necessarily so. I had a thread some time back that pointed out some of the inconsistent apportionments that have occurred -- mainly in reply to threads bemoaning the "unfairness" of caucuses. I would guess that because of the quirkiness in apportionment, Hillary will actually have to do better than 65% in popular vote to actually attain 65% of the available delegates.