I just tried to go on the Omani e-visa page and the very first time, I was offered the option of applying for a multiple-entry visa (valid 1 year for 30 days per visit) for 50 rials, but subsequently no matter what I do I can't get the website to give me that option again, and only the single-entry visa for 20 rials is available.
I think the e-visa pages might have some bugs. I checked the flashy new portal, where it gives you the visa types available to your passport and country of residence: the UK does not allow multiple entry visa, though the preceding text says it should, as a G1 country. And other G1 passports are offered this facility. So it's probably a "feature" yet to be ironed out.
The old website still contains visa forms for completion:
https://www.rop.gov.om/visa/english/...tion_main.aspx