Calgary-based WestJet, which flies to 80 cities in North America, is the latest carrier to introduce a premium economy seating product.

The company said work is starting this month on a reconfiguration of its fleet that will add four rows of seats with 36 inches of pitch. Travelers who buy those seats will also get priority boarding and “complementary on-board amenities,” the company said. The installations should be finished by December 2012.

In order to accommodate the extra legroom in those rows, “WestJet will also standardize the seat pitch for the remaining rows on all aircraft to 31 to 32 inches, bringing its seat pitch in line with North American competitors,” the company said.

That 31-32-inch pitch is already standard on WestJet’s 737-600 and -700 aircraft, but the change will mean that pitch on its 17 737-800s will shrink down from the current 34 inches. In addition, some 737-600 and -700 aircraft with 32-inch pitch will reportedly see that number shrink to 31 inches, according to Canadian media reports.

WestJet’s fleet includes a total of 100 aircraft, all of them 737-600s, -700s and -800s. It will take delivery of another 36 next-generation 737s through 2018.