In 2001 the international auditing practices committee (iapc, now the international auditing and assurance standards board (iaasb)) commissioned research on the determination and communication of moderate assurance. This research was published in ifac research monograph no. 1 (2002). Part of this research involved surveying the types of assurance services undertaken by 56 assurance firms from 11 different countries, the levels of assurance at which these assurance services were generally provided, and for those services provided as moderate assurance services, the reasons why. This paper re-analyses this data and extends the ifac research report (2002) by examining the differences between the types of assurance services (other than historical financial statement assurance) and levels at which these assurance services are provided by the former big 5 audit firms compared with the non-big 5 audit firms. Information was also collected on 166 moderate assurance engagements provided by these participating assurance firms. The determinants of the level of assurance for these assurance service engagements were identified and differences between the big 5 and the non-big 5 audit firms are reported.