So many fares, so many rules. How did your seatmate pay a lower fare than you? Why did you have to stay over a Saturday night? What constitutes a non-refundable ticket? Knowing what types of airfares exist, and how they apply to your travel, will not lead you to believe that airfares make sense, but you can at least make some sense of them.

The types of fares, rules and restrictions, taxes and security charges are all components that complicate the price involved for a passenger to fly from one place to another.

Fares are most often based on one-way or round-trip travel. They may be published, unpublished or privately negotiated.

• A published fare is one that is available for purchase by the public, by anyone. If you called the airline, checked for prices online or contacted your travel agent, the published fares could be purchased immediately.

• Unpublished fares are are not offered for sale by the airline, neither online or over the phone. They may be seats that a consolidator purchased in bulk from the airlines and offers through travel agents or directly to the public at highly discounted rates. (Check out those small-print ads in this travel section for scores of irresistible consolidator fares.) The fare rules regarding these tickets are likely to be highly restrictive and should be investigated thoroughly by the prospective purchaser.

• Negotiated fares, generally very favorably priced, are those agreed upon by contract between the airline and a second party, such as a cruise line, tour operator, corporation or government agency. The tickets are made available in private transactions to purchasers deemed eligible by the contracting organization.

Regardless of whether a ticket is issued under a published or unpublished fare, it reflects a letter of the alphabet that is assigned to different types of fares. These letters indicate the class of service, not just economy or business or first class, but rather the type of fare that was purchased. These fare indicators (that appear following the flight number on a ticket, like DL 316 K) may vary by letter and in value among different airlines.

F, P and A are the letters typically used to indicate first class.

Business class is commonly indicated by J, C, D, I and Z.

Y is almost universally used to indicate a full-fare economy ticket. B, M, Q, V, H, L, and K are just some of the letters indicating subclasses within economy — reduced, restricted and/or discounted fares. X, U and R are a few of the letters that indicate consolidator fares.

Following are descriptions of the main types of published airfares, based on round-trip or one-way travel, and targeting the leisure traveler:

• An APEX (Advance Purchase Excursion) and Superapex international fare is generally the lowest priced and most heavily restricted. It could, for example, be a non-refundable, capacity-controlled fare requiring an advance purchase of seven to 52 days and a minimum Saturday night stay.

• Discount fares tend to have a smaller price tag and limited-time offering, such as an airline seat sale. They usually bear a long list of restrictions such as specific travel dates, minimum and maximum stay, etc. Like most published fares, it is important to determine the fare rules and restrictions on discount fares.

• Excursion fares are lower priced fares that involve restrictions like advance purchase, time of year and minimum/maximum stay.

• Full fares apply to the most flexible, expensive tickets. This fare is the normal, undiscounted fare quoted for travel from point A to point B, and it has no restrictions except a 365-day validity. It can be purchased at any time; it is fully refundable; it allows a reservation to be changed at any time without penalty; it has no minimum or maximum stay; and it is valid for one-way or return travel.

• Joint fares are offered by two or more airlines that have formed a partner relationship on certain routes. Although offering a price break to the passenger, joint fares come saddled with their own set of restrictions to observe.

• A through fare is a fare to a destination reached by traveling through a gateway city, such as from Honolulu through Atlanta to reach Miami. It could be combined with any of the fare types listed above, and is used to obtain a lower price when you cannot simply fly from point A to point B, but must connect through other points to arrive at your destination.

A new fare model, used by Southwest, Air Canada and other carriers, consists largely of one-way fares that are lowest when purchased 14 or more days in advance.

Airlines, under the machinations of their yield-management specialists, will not offer every seat on an aircraft at a reduced fare. As flights book up, the least expensive fares disappear, regardless of how far in advance it is. The closer to departure on a popular flight, the more you will pay for a seat. If a flight is showing a light load a couple of weeks prior to departure, the airline may offer a "last minute" seat sale. In general, you are likely nowadays to pay less for a ticket the earlier you buy it. However, the truly aggravating consequence of early purchase is that a fee of $50 to $150 will be imposed by the airline if you want to change your ticket to take advantage of a cheaper fare offered after your original purchase.

Unless you are buying a pricey full-fare ticket, be assured there will be any number of restrictions that apply to and affect the bottom line of your airfare. Determine the flexibility of your proposed ticket before payment. Your travel professional will be able to advise about rules affecting different fares and can secure the best-value tickets consistent with your travel plans.

Irene Croft Jr. of Kailua, Kona, is a travel writer and 45-year veteran globetrotter. Her column is published in this section every other week.