Requirement to fly an Ovstacle Deeparture Procedure

[LOKE]

This question refers to US rules - I'm not sure what JAROPS calls these things.

If there is an ODP - obstacle departure procedure - at a field and your clearance does not specify a SID, or there is not SID, are you required to fly the ODP?

Can't find a specific reg that covers it and of course I'll be looking a long time if there isn't one.

Thanks for any information that you can provide,

LOKE