Objectives: To identify variation in patient, event, and scene characteristics of out-of-hospital cardiac arrest (OOHCA) patients assessed by emergency medical services (EMS), and to investigate variation in transport practices in relation to documented prehospital return of spontaneous circulation (ROSC) within eight regional clinical centers participating in the Resuscitation Outcomes Consortium (ROC) Epistry. -Cardiac Arrest. Methods: OOHCA patient, event, and scene characteristics were compared to identify variation in treatment and transport practices across sites. Findings were adjusted for site and standard Utstein covariates. Using logistic regression, these covariates were modeled to identify factors related to the initiation of transport without documented prehospital ROSC as well as survival in these patients. Setting: Eight US and Canadian sites participating in the ROC Epistry. -Cardiac Arrest. Population: Persons ≥20 years with OOHCA who (a) received compressions or shock by EMS providers and/or received bystander AED shock or (b) were pulseless but received no EMS compressions or shock between December 2005 and May 2007. Results: 23,233 OOHCA cases were assessed by EMS in the defined period. Resuscitation (treatment) was initiated by EMS in 13,518 cases (58%, site range: 36-69%, p< 0.0001). Of treated cases, 59% were transported (site range: 49-88%, p< 0.0001). Transport was initiated in the absence of documented ROSC for 58% of transported cases (site range: 14-95%, p< 0.0001). Of these transported cases, 8% achieved ROSC before hospital arrival (site range: 5-21%, p< 0.0001) and 4% survived to hospital discharge (site range: 1-21%, p< 0.0001). In cases with transport from the scene initiated after documented ROSC, 28% survived to hospital discharge (site range: 18-44%, p< 0.0001). Conclusion: Initiation of resuscitation and transport of OOHCA and the reporting of ROSC prior to transport markedly varies among ROC sites. This variation may help clarify reported differences in survival rates among sites and provide a target for identifying EMS practices most likely to enhance survival from OOHCA. © 2010 Elsevier Ireland Ltd.