Statutory Account Books — Which Set Your Station Needs

Statutory account books (ก, ข, ค) is a phrase every fuel station owner hears from their accountant whenever accounting fees come up — yet many are never quite sure how the sets differ, which set their station actually needs, and who gets to inspect them. This article explains it from the legal root through to the real payoff: seeing true profit per liter at your station.

First, separate two things. The accounting the law actually requires is the 8 statutory book types under the Accounting Act (พ.ร.บ.การบัญชี พ.ศ. 2543). The labels ก, ข, ค, on the other hand, are trade jargon accountants use to describe how complete the accounting work is — that naming appears nowhere in the act itself. Once you hold these two layers apart, comparing accounting service quotes becomes an apples-to-apples exercise instead of an upsell.

1. The law sets a minimum of 8 statutory book types

Under the Accounting Act, a legal entity must keep all 8 book types: the asset register, liability register, owners' equity register, income register and expense register, together with the daily cash receipts book, daily cash payments book and daily sales book. The books must be kept at the place of business, accounts closed on a 12-month cycle, and the books together with supporting documents retained for no less than 5 years from the closing date. Today a computer accounting program generates all 8 book types automatically — but the quality depends on the on-site data fed into it.

2. What separates sets ก, ข, ค is the depth of the accounting

The set labels don't change what the law requires — they signal how granular the accounting is. Roughly speaking:

• Set ก — legally complete: all 8 book types plus basic financial statements, enough for tax filing, but you can't drill into much detail
• Set ข — adds sub-accounts to the general ledger: expenses split into finer categories, receivables split by customer group — you see where the numbers come from
• Set ค — a yet more granular ledger, e.g. cost of sales tracked per fuel grade, with analytical reports for management

3. Which set should a fuel station keep?

Set ก is the legal minimum, but a station with several tanks, a convenience store and corporate receivables should run at least Set ข, because you need to know which fuel grade actually makes money. Do the simple math: a station selling 300,000 liters a month with a 0.10-baht-per-liter margin gap between grades is looking at a 30,000-baht monthly difference. If the books don't split by grade, the owner will never see that gap — pricing and promotion negotiations with the oil company stay guesswork forever.

4. Book certification for computer accounting from ETDA

If the station runs a computer accounting system, choose software that has been certified by the authority empowered to issue book certification — the Electronic Transactions Development Agency (ETDA) — under the announcement on accounting practice. A certified system has data controls, audit trails and report reliability that meet the prescribed criteria, which makes the numbers in the statutory books easier to accept when the books come under review. Before buying any accounting program, always ask to see its ETDA certification number.

5. Who inspects the books, and within how many days?

The legal authority to inspect the books sits with officials at the Provincial or Area Revenue Office level. If the station receives a notice to submit its books for inspection, the books and supporting documents must be presented within 5 days of receiving the notice — missing the deadline carries a legal penalty. Having a system that keeps documents complete and the books in order is not a luxury; it is a state of readiness you must maintain at all times, because the notice does not book an appointment in advance.

6. What complete accounting means for tax

Correctly kept statutory books are the primary evidence that lets tax law accept the business's expenses. One condition owners should know is the expense-to-asset ratio: if expenses in the nature of cost and expenses paid to external creditors exceed the prescribed ratio (a rule of thumb of 25% per year), the excess may be disallowed as a deductible expense. However, a legal entity using a computer accounting system certified under accounting law is exempt from this condition by statute. The technical details are complex and shift year to year, so always have your accountant or tax advisor confirm against your station's actual case.

7. How sets ข and ค reveal true profit per liter

The real selling point of granular accounting is turning book numbers into decisions. For example: gross margin of 1.20 baht per liter, minus operating expenses of 0.90 baht per liter, leaves pre-tax profit of 0.30 baht per liter. Numbers like that answer instantly which promotions pay off and which expense lines need reining in. How to read these figures is covered in detail in how to read a fuel station P&L.

In short: every station must keep all 8 statutory book types, sets ข and ค raise the granularity so the owner sees numbers they can actually decide with, and documents must be ready for submission to the Provincial Revenue Office within 5 days of notice. If you want on-site sales and stock flowing into the books in good order, see our fuel station accounting software for the ก ข ค statutory books, and the whole-of-system tax picture in fuel station taxes in Thailand — the owner's overview. That said, a station's accounting should always be supervised by a bookkeeper qualified under the law.