The ACT Auditor-General's report, tabled in June this year, examined credit card use across all territory public agencies last year, finding the ACT public service charged between $456,000 and $599,000 a month to credit cards in 2015.

It found the Education, Health and Justice and Community Safety directorates were the three biggest spenders, but some smaller agencies were more frequent credit card users.

The audit also revealed a marked discrepancy between the size of individual agencies and the number of credit cards they had issued to them.

Of the larger directorates, staff in the Education Directorate Schools, Health and Justice were issued with 70, 61 and 74 credit cards respectively in 2015 - compared to the 4303, 6195 and 1529 total full-time staff each agency employed last year.

But the audit showed there "was not a correlation between the number of staff in the entity and the number of cards".

The report revealed the Cultural Facilities Corporation had 14 of its 90 staff issued with a card, or about 15 per cent of all staff, on which $184,158 was spent in 2015.

Similarly, the ACT Building and Construction Industry Training Fund Authority, with only three employees, was issued with two credit cards, to which it charged $6,599 worth of supplies.

The report revealed the authority's charges came to about 10.5 per cent of its total "supplies and services expenditure" for 2015, the highest share charged to credit cards of any ACT government agency.

Analysis also found the Cultural Facilities Corporation, the Building and Construction Industry Training Fund Authority and the Public Trustee for the ACT had the "highest number of monthly statements per credit card", indicating more frequent use in those agencies than other directorates.

The lion's share of the ACT government's 2015 credit card bill, was spent by the Education Directorate Schools, spending $1,782,291 on official cards - or 28.45 per cent of the total expenditure charged to credit cards that year.

Both the Health Directorate and the Justice and Community Safety Directorate spent between $790,000 and $760,000, followed by the Canberra Institute of Technology, which spent $625,185 or just shy of 10 per cent of the ACT's total credit card bill.

Chief Minister Andrew Barr's directorate was the fifth biggest-spending department, racking up $570,811 on the department's cards - or about 9 per cent of the ACT government's total bill.

The Auditor-General's report said credit card expenditure represented a "very small component" of the total ACT government supplies and services expenditure in 2015, and most transactions were small - 39 per cent - or 1601 of the 4128 transactions examined were for $500 or less in 2015.

It also reported transaction limits were being "effectively managed" and all ACT government entities except the Land Development Agency had "satisfactory or good guidance" regarding the need for documentation to "support the use of the credit card".

The audit urged the ACT government review "at least annually" all credit cards with a view to rescinding those not being used, and recommended all departments provide better guidance to staff on the use of cards and need for supporting documentation for claims made.

While all ACT government bodies were approached to respond, only Elections ACT did so, pledging to complete an internal review of its "financial instructions on credit card use" in the 2016-17 fiscal year.