Until recently, if you were sued for patent infringement, the case was most likely to be filed in the Eastern District of Texas. But this year, the District of Delaware is on track to overtake East Texas as the nation's most popular venue for filing patent lawsuits. There have been 1,015 patent lawsuits filed in Delaware, compared to 920 in the Eastern District of Texas.

Even more striking, these two districts have accounted for a skyrocketing share of all federal patent lawsuits. So far in 2013, they have accounted for 45 percent of all patent lawsuits. That's a record high, and it's way up from a decade ago, when fewer than 10 percent of patent cases were filed in these two districts:

(James Pistorino)

These statistics were compiled by James Pistorino, an attorney at the law firm of Perkins Coie. He says the trend gives the 10 judges who hear cases in those two districts an outsized influence over patent law. And the trend has likely made the system more friendly to patent lawyers.

"These are judges that at least the plaintiffs believe have procedures that are more favorable to them than in other districts," Pistorino argues. For example, defendants benefit when judges quickly weed out frivolous claims with summary judgment motions. But Pistorino says that judges in Delaware are relatively slow to rule on summary judgment motions. That raises the cost of litigation for defendants, giving plaintiffs more leverage in settlement negotiations.

So the shift of patent litigation to Delaware and East Texas doesn't just mean that patent defendants are increasingly forced to travel to courthouses far from home. It's also subtly tilting the patent system against defendants, by giving some of the nation's most plaintiff-friendly judges a disproportionate role in deciding patent disputes.