I've been scratching my head on this one for awhile here. In a carbonyl sulfide (COS) molecule, what is the hybridization state of oxygen?

Carbonyl sulfide is composed of a single carbon atom double bonded to oxygen and sulfur atoms. The sulfur and oxygen atoms each harbor two lone pairs.

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Looking at oxygen, I count electron-dense groups:

  • There is one bonded atom
  • There are two lone pairs

This should amount to an sp2 hybridized orbitals for oxygen, before exceptions are accounted for.

Checking if any lone pairs are delocalized:

  • Oxygen both participates in a pi-bond and is adjacent to a carbon that participates in a pi-bond

This is where I'm stuck. Are any of oxygen's lone electron pairs delocalized due to these facts? Is the hybridized orbital not sp2 for oxygen?