Can an Oklahoma LLC operate under multiple trade names?

Yes, an Oklahoma LLC can operate under multiple trade names. You file a Trade Name Report with the Secretary of State for each name you want to use. Each one is a separate filing. Your legal name on file is still the LLC. The trade name is just a DBA.

FYI I think the filing was $25 per name when I did mine last year. Not free but not terrible.

Does the trade name have to be tied to the LLC specifically, or can a sole proprietor file one too? I'm asking because I've been thinking about doing this for a side project that isn't part of my LLC.

Sole proprietors can file a trade name in Oklahoma too. The filing form just asks for the entity name, so if you're a sole prop you'd list your own name as the owner. Different situation than what the OP is doing but yes it's allowed.

Bank will probably want to see the trade name filing paperwork before letting you endorse checks under that name. Some banks are picky about it. Call yours first instead of walking in with a check and hoping.

On the insurance point since OP asked. Your general liability policy is written under the LLC. If a crew member or a customer is doing business with the pressure washing name and something happens, the claim still goes back to the LLC. But you should tell your agent the trade name exists so the policy references it. Some carriers will list DBAs on the policy, some want a separate endorsement. Don't skip this. If you're sued under the trade name and the policy only names the LLC, there can be a coverage fight.

The insurance part is more of a paperwork headache than anything else, but GreenTerraSooner is right that it's worth doing. The trade name doesn't create a seperate legal entity so you're not suddenly insuring two businesses. It's one LLC, one policy, just make sure the DBA shows up somewhere.

Taxes: nothing changes at the federal level. Single member LLC files Schedule C under your own SSN or works through the LLC if you're taxed as a partnership or S corp. The trade names don't get separate EINs. Some people make the mistake of getting a new EIN for each name and then wonder why their filings are a mess

I don't believe there's a cap. It's just a filing fee each tims. That said I'd keep it reasonable. Every name is one more thing to renew and one more thing to keep straight on insurance and bank paperwork. If one of the names goes dormant you should be thinking about whether to keep it active.

Renewal is the part people forget. The trad name registration isnt permanent forever. Oklahoma requires it to be renewed periodically, I want to say every few years but check the current schedule with the Secretary of State because they've changed it. If it lapses you lose the exclusive right to use that name in the state and someone else can file it.

Also make sure the name you pick for pressure washing isn't already taken. The SOS search is free and quick.

One thing nobody has brought up: trade names don't give you trademark protection. Filing with the Secretary of State just registers the name for state-level business use and stops someone else from registering the identical name with the SOS. It does not stop a competitor from using a confusingly similar name, and it does not give yoj federal rights. If the pressure washing brand actually grows, talk to an attorney about a trademark down the road. Different system entirely.

You can also cheeck whether your city or county requires the trade name on any local license or permit. Pressure washing might fall under a separate local permit in some municipalities even when the LLC is fine at the state level. State registration doesn't automatically satisfy local requirements.

Right. State filing and city licensing are two different checkboxes. Neither one covers the other.