Envoy Air, formerly called American Eagle, first instance, is easily the biggest offender. For every 1,000 passengers, the airline mishandles roughly nine bags. ExpressJet, the second biggest offender, mishandles just under six bags for every 1,000 passengers. And Southwest Airlines, American Airlines, and United, meanwhile are fifth, sixth, and seventh, respectively, on the list; each at rate closer to four bags per 1,000 passengers.
These percentages might not seem all that high, because they somewhat undershoot the actual rates at which airlines are losing or at the very least mishandling peoples' bags. The government computes the mishandling rates by pitting lost luggage against all enplaned passengers—not merely those who checked in luggage. Of course, many passengers carry their luggage along with them, or travel with little to no luggage at all—especially given the rise of checked bag fees.