Common Verbs:
* Open
* Offer
* Obtain
* Observe
* Occur
* Operate
* Order
* Organize
* Overcome
* Owe
Less Common Verbs:
* Oblige
* Obscure
* Occupy
* Offend
* Omit
* Oppose
* Outdo
* Outgrow
* Overflow
* Overlook
* Overrule
Phrasal Verbs:
* Outgrow
* Outlive
* Outpace
* Outshine
* Overdo
* Overlook
Specialized Verbs:
* Obviate
* Oscillate
* Officiate
* Opine
This is not an exhaustive list, but it provides a good starting point for verbs that begin with the letter "O."