obcecar / to blind

obedecer / to obey

objetar / to object

obligar / to force, to compel, to oblige

obliterar / to obliterate, to erase

obrar / to build, to work

obsequiar / to give a gift

observar / to observe

obsesionar / to obsess

obstinar / to insist

obtener / to obtain, to get

obturar / to block

ocasionar / to cause

ocupar / to occupy

ocultar / to conceal

odiar / to hate

ofertar / to offer

oficiar / to officiate

ofrecer / to offer

ofrendar / to offer (religioso)

ofuscar / to dazzle (brillo/sol), to blind (celos)

oír / to hear

ojear / to look at

oler / to smell, to scent

olfatear / to smell, to sniff

olvidar / to forget

omitir / to omit

ondear / to ripple

ondular / to wave

opacar / to make opaque

operar / to operate, to perform a surgery

opinar / to opine, to think, to have an opinion

oponer / to oppose

opositar / to take a competitive examination

oprimir / to press, to push (botón)

optar / to opt, to choose

optimizar / to optimize

orar / to pray

ordenar / to arrange, to order, to command (mandar)

originar / to originate

organizar / to organize, to set up, to arrange

ornar / to adorn

ornamentar / to decorate

osar / osar + infinitive = to dare + infinitive

oscilar / to oscillate, to swing

oscurecer / to get dark, to grow dark

otorgar / to grant