To determine if a cruise ship is sailing at full capacity, the most reliable method is to perform a "mock booking" on the cruise line's website. By going through the steps of selecting a cabin for your specific date, you can see which categories are marked as "Sold Out." If only a few individual cabins remain available for selection on the deck plan, the ship is nearing its limit. Additionally, cruise lines often report their "occupancy percentage" in quarterly financial statements; "100% occupancy" usually means two passengers per cabin (lower berths), but because many rooms hold three or four people, ships often sail at 105% to 110% capacity. Another indicator is the availability of "Bid for Upgrade" programs; if the airline or cruise line isn't sending out emails for cabin upgrades, it usually means there is no unsold inventory to move people into. Finally, travel agents have access to "GDS" systems that show real-time cabin availability, so a quick check with an agent can provide a definitive answer on how close a specific sailing is to being completely booked.