[dartland]

Yes and no. Price is relative to demand. If the plane fills up ahead of expected, demand is assumed to be higher and prices will go up. If the plane is more empty than predicted, fares will fall. Competitor moves can also impact this.

But even aside from that, prices go up as the cheaper fare classes get sold out. This isn't the airline raising fares, it is simply the cheap seats get sold out.

Finally, there are fare rules. The cheapest fares generally have 14 or 7 day advanced purchase requirements. So without touching anything, fares will go up at those time increments as the cheapest fares are no longer available, even if seats are still available. This is to protect the airline from selling cheap seats to last-minute business travelers with a high willingness to pay.