Bigger catchment areas are needed to give people more choice when it comes to choosing a GP practice, according to a think-tank.
Reform Scotland also said all surgeries should have a website and provide clearer information for patients.
It made a series of recommendations it believes would give patients greater choice in picking a practice which provides services suited to them.
In a report, the independent organisation said research showed where you live will often determine whether you can attend an evening or weekend surgery, or order repeat prescriptions online. By expanding a practice's catchment area, Reform Scotland believes patients will be provided with a meaningful choice which will drive up standards.
Director Geoff Mawdsley said: "Reform Scotland believes that it is simply unacceptable that there is such a wide variation in the way people can access GP services, whilst there is little or no choice over where they can register."
The paper, Patients First: Improving access to GP practices, also recommends allowing new surgeries to open up to further increase choice and improve services. It said it believes the ban on private sector companies opening GP practices should end. However, doctors' leaders said they disagreed strongly with the recommendations.
Dr Alan McDevitt, chairman of the British Medical Association's Scottish general practitioners committee, said while the report had picked up on the important issue of access, he "could not disagree more" with their proposed solutions.
"What some call postcode lottery others would call local flexibility. A proportion of services provided by practices are agreed locally between the health board and individual practices according to local priorities," he said.
"In the case of extended hours, for example, what is the point of a GP spending time running a late surgery if there is no demand for it locally? We will always have to work to improve access as there is no 'perfect' solution."
But Mr Mawdsley said expanding the catchment area would not put extra pressure on practices as they would still be able to close their lists to new patients if they reached capacity.