Looking on the internet deeply has found these results:

Advisor is the most popular phrase on the web.

Adviser 15,640,000 results on the web	Advisor 1742,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
In the UK, Ireland and Asia the spelling is traditionally adviser, though US spelling advisor is becoming increasingly common. In the US, Associated Press style�... adviser. (?d?va?z?) or advisor. n. 1. a person who advises. 2. (Education) education a person responsible for advising students on academic matters, career�... An adviser or advisor is normally a person with more and deeper knowledge in a specific area and usually also includes persons with cross functional and�... Adviser and advisor are both accepted spellings of the noun meaning one who advises or counsels. There is no difference between them. But adviser, the older �...	Shigenori Takano and Tsutomu Ando shall cooperate with the organization as its Consul and Supreme Advisor. Assad for strategic questions and military intelligence. Cummings is the President's Chief Advisor. He's a kind of... Advisor. Advisor to President Bashar Al Robert Bailey, Policy Advisor at Oxfam International. Senior Advisor at the Central Bank (Banco de Portugal). I understand you're acting as Special Advisor to your successor.

Adviser

15,640,000 results on the web

Advisor

1742,000,000 results on the web

More popular!

In the UK, Ireland and Asia the spelling is traditionally adviser, though US spelling advisor is becoming increasingly common. In the US, Associated Press style�...
adviser. (?d?va?z?) or advisor. n. 1. a person who advises. 2. (Education) education a person responsible for advising students on academic matters, career�...
An adviser or advisor is normally a person with more and deeper knowledge in a specific area and usually also includes persons with cross functional and�...
Adviser and advisor are both accepted spellings of the noun meaning one who advises or counsels. There is no difference between them. But adviser, the older �...

Shigenori Takano and Tsutomu Ando shall cooperate with the organization as its Consul and Supreme Advisor.
Assad for strategic questions and military intelligence.
Cummings is the President's Chief Advisor.
He's a kind of... Advisor.
Advisor to President Bashar Al
Robert Bailey, Policy Advisor at Oxfam International.
Senior Advisor at the Central Bank (Banco de Portugal).
I understand you're acting as Special Advisor to your successor.