Can I run OO trains on OO9 narrow gauge tracks?

It is not possible to run standard OO gauge trains on narrow gauge track as OO gauge needs to run on 16.5 mm track and OO9 narrow gauge runs on 9mm track, which is the same as N gauge track.

OO9 stands for, as the name suggests, OO scale and 9mm. The body of the engine, wagon or coach is OO scale (1/76) while the wheels are spaced 9mm.

So the chassis of the engine needs to be able to run on the narrower track than standard OO gauge.

You can run N gauge trains on OO9 track and OO9 trains on N gauge track. In both cases, the track width is the same but the sleeper spacing will be incorrect.