PRASM (Passenger Revenue Per Available Seat Mile)

PRASM is one of the most important operating metrics in the airline industry. It normalizes passenger revenue against the amount of capacity deployed — measured in available seat miles — allowing analysts to compare airlines of different sizes and assess whether a carrier is growing revenue in proportion to, ahead of, or behind its capacity expansion.

An available seat mile (ASM) represents one seat transported one mile, regardless of whether it is occupied. Total ASMs for a flight equal the number of seats on the aircraft multiplied by the route distance. PRASM divides total passenger revenue by total ASMs for a period. A carrier with $20 billion in passenger revenue and 200 billion ASMs has a PRASM of 10 cents.

Delta Air Lines, American Airlines, and United Airlines all report PRASM as a primary yield metric. For major US network carriers, PRASM is influenced by the mix of routes flown (transatlantic premium routes carry higher PRASM than domestic leisure routes), the proportion of premium cabin seats, fuel surcharge recovery, and the effectiveness of revenue management systems in filling seats at maximum prices.

PRASM can be disaggregated into two components: yield (average fare per passenger mile flown) and load factor (percentage of available seats occupied). PRASM equals yield multiplied by load factor. An airline can improve PRASM by raising fares — if demand allows — or by filling more seats, or ideally both. Revenue management systems are designed to optimize this product dynamically across thousands of routes and booking windows simultaneously.

Comparing PRASM against cost per available seat mile (CASM) reveals the unit economics of the airline at the operating level. When PRASM comfortably exceeds CASM, the carrier is generating positive unit operating profit. When the two converge or CASM exceeds PRASM — as can happen during fuel price spikes or sharp demand downturns — the airline operates at a unit loss and must either reduce capacity or absorb losses until conditions improve.

Investors analyzing airline stocks track PRASM trends relative to capacity growth (expressed as ASM growth) and competitive route dynamics. An airline aggressively growing capacity in a market where fares are under pressure from competitors risks diluting PRASM even if total revenue grows. Revenue-per-available-seat-mile performance in long-haul international and transatlantic premium routes is particularly scrutinized because those routes tend to carry disproportionate revenue and margin contribution.