Call-Out Service Contracts have become an important contractual instrument in oil and gas drilling projects, enabling rapid and flexible access to specialized services under conditions of technical, operational, and temporal uncertainty. Despite their widespread use, their legal nature and binding effects, particularly under Iranian law, have received limited systematic analysis. The principal question addressed in this study is whether a Call-Out Service Contract creates legally binding obligations upon its conclusion or whether the relevant obligations arise only upon the issuance of a Call-Out Order. Adopting a descriptive-analytical methodology with a comparative approach, the study examines the issue primarily under Iranian law, while drawing on English and U.S. law where appropriate. The findings indicate that, where the parties have agreed on the essential elements of the relationship and provided sufficient criteria for determining variable obligations, a Call-Out Service Contract should generally be regarded as a binding framework agreement. Accordingly, it may create obligations of readiness, availability, responsiveness, and compliance with contractual requirements before any specific Call-Out Order is issued, while the performance of particular services and certain related payment obligations may be activated by such an order. The mere fact that the precise timing, quantity, or frequency of future services remains undetermined does not necessarily invalidate the contract, provided that adequate mechanisms exist for determining those elements. The study further analyzes the implications of this legal characterization for contractual chains, payment mechanisms, contractual liability, delay, back-to-back arrangements, and risk allocation.