Not enough GPs have a website or allow appointments to be booked online, according to a Scottish think tank.
Reform Scotland says a third of GPs are still not on the web and 90% only accept bookings in person or over the phone.
Just over half of the nearly 1,000 surgeries in Scotland allowed online ordering of a repeat prescription.
Less than 40% advertise extended opening hours on a website.
Four years ago, a report by the Royal College of General Practitioners and the Scottish government said online appointments would improve patients' access to GPs.
Reform Scotland, a think tank which looks into public services, said the variation in the way people can access GPs has nothing to do with size or geography.
It argues they should be allowed to find a practice which provides services their existing GP does not.
Director Geoff Mawdsley said: "We believe that giving individuals greater choice over their GP practice would mean that people were able to easily walk away from GP practices they felt did not provide services that suited them.
"We don't envisage that such a policy would lead to a mass exodus of patients from GP practices.
"But the potential that they could would give them much greater influence over the way services developed."
The Scottish government said online services are currently available to all GP practices in Scotland and it was "continuing to work to promote and encourage practices to use these services".
A spokeswoman said: "While there are more doctors per head of population in Scotland than across the rest of UK and we are investing in primary care services, we accept that we must do more to make access to GPs even easier.
"That is why we have committed to a review of patient access to General Practice and invested £1m to support a programme which will work with health boards across Scotland to trial new models of care.
"We have also already negotiated a new contract with GPs that dramatically cuts bureaucracy, freeing up GP time for patients.
"This isn't the end of the process and we will now work with GPs to improve the contract even further and ensure primary care services are as well prepared as possible for the challenges of the future."