This study examines the relation between size of audit firm and audit quality, and the choice of accrual measures for a large sample of firms. In relation to the impact of different sizes of audit firms on audit quality, a clear majority of oil companies and audit firms agreed that Big Four firms are superior to their non-Big Four counterparts in all of the reputation issues presented to them, and that the size of the audit firm is positively associated with audit quality. Such superiority is seen in terms of resources and audit technology, and the consequent motivation to perform as professionally as possible. A questionnaire was used to collect data. To confirm and support the questionnaire findings, semi-structured interviews were conducted. The data used for this study were collected from two sources: the demand side (Libyan oil companies) and the supply side (audit firms working in Libya). The data for the Libyan oil companies were gathered from three different types of respondents: internal auditors, financial managers and accounts managers. For the audit firms, data were gathered from employees at all levels in the firm: managing partners, audit supervisors and auditors