Several callers were puzzled by a brief wire story on our Business section cover on Monday, citing Lundberg Survey numbers showing San Diego drivers paying the highest prices for gasoline in the nation — $3.12 a gallon.

They asked: Weren't parts of Hawai'i paying more than that?

And they were right, of course. Just a few days earlier, we had reported Hilo drivers paying an average $3.197 a gallon and Wailuku drivers paying $3.415. And certainly, there are prices in other areas in the Islands that are even higher.

So, yes, while that story accurately reported Lundberg's national average price, it clearly did not reflect the higher prices drivers are paying here.

Even aside from that blip, reporting on gasoline prices presents some challenges.

Part of the challenge is that there are two sets of numbers we — and readers — pay attention to.

One is the gas price cap, which is calculated each week by the state Public Utilities Commission and is a state-set ceiling on wholesale prices. The gas cap is based on wholesale prices during a five-day period in three Mainland markets.

The gas-cap law does not regulate retail prices. As this was written, lawmakers were considering whether to abolish or amend that law.

The other number is the average retail prices for gasoline.

For those numbers, we rely on AAA's Daily Fuel Report. AAA get its numbers from the Oil Price Information Service, and the numbers are updated daily and are posted for regular, mid, premium and diesel.

AAA calls its numbers the most comprehensive retail gasoline survey available. It surveys prices in all states and the District of Columbia.

The report is compiled from prices at up to 85,000 self-service stations nationwide. In Hawai'i, 237 stations are surveyed. Each day's prices are based on the last credit-card swipe at each station the previous day.

It is certainly the best data set available to us, and the numbers are also cited by government agencies.

In addition to current prices, AAA also provides comparisons with prices a year earlier and posts the highest recorded price in each area surveyed.

The caveat is that for Hawai'i, average prices are available for just Honolulu, Hilo and Wailuku. AAA also provides a statewide average for Hawai'i based on the three areas it surveys as well as stations in other areas. For example, while an average price for Kaua'i is not provided, there are some Kaua'i stations surveyed for the statewide average.

We publish the latest AAA numbers every Wednesday, noting the year-earlier numbers and the highest ever for comparison.

Readers on other islands often call wondering why we do not publish average numbers for their islands.

We would certainly use numbers for other areas if they were available, but right now they are not. We definitely are aware there are areas with higher averages, and if they ever become available, we will report them.

Reach Anne Harpham at aharpham@honoluluadvertiser.com.