Act fast to get a free companion pass on Southwest Airlines.

Southwest Airlines is offering its Companion Pass promotion again, allowing Rapid Rewards members to bring a friend for free on an unlimited number of flights between August 15 and September 30. To qualify, members must register for the promotion and purchase a flight before May 24, with the catch being that flights must be booked by Wednesday night. The promotion cannot be applied to flights booked before registration, and the free ticket does not include taxes and fees. Members can also earn a Companion Pass by racking up 135,000 points or flying 100 qualifying Southwest flights within a calendar year.