Patients reported a poorer experience of care from commercial providers than from non-profit organisations in the study published in the BMJ.
Minority ethnic patients and those unable to take time away from work reported the worst experiences of care.
GP leaders said politicians should learn lessons and move away from greater private sector involvement.
Commercial GP providers
The researchers said more work was required to better understand the reasons for the findings. Professor John Campbell from the University of Exeter Medical School, who led the research team, said it was important to exercise caution interpreting the results.
‘Although commercial providers scored lower overall, the best commercial providers scored higher than many of the NHS and not-for-profit providers,' he said.
‘There are variations and examples of good practice among all providers, but the overall trend is that patients report less positive experiences with commercial providers, and we now need to understand why that is the case.’
The researchers analysed GP patient survey data from 80,000 patients who had had contact with GP out-of-hours services in the preceding six months, their experience of care, and the type of provider organisation.
Quality of GP care
GPC deputy chairman Dr Richard Vautrey said there was evidence of a division in quality between those services developed by GPs co-ops and private providers.
‘Services with roots in the NHS often retain their connection with local GPs who continue to work evenings and weekends, providing a strong line of continuity and connection with patients,' he said.
‘GPs in these working arrangements often have a greater say in how services are delivered, which takes into account the needs of the local community. This positive environment does not always exist in contracts delivered by the commercial sector.’
Dr Vautrey called on politicians to learn lessons and move away from greater private sector involvement in the NHS and address the problems of inadequate funding.
A spokeswoman for commercial provider Care UK, however, said the firm did not recognise the findings for the services it provides in the NHS. 'In the last two months, between 92% and 93% of the patients surveyed told us that they would be happy to recommend the service to their friends or family,' she said.