speculate on something
speculate about something

One can only speculate about the use made of the park.

But he doesn't want to speculate about the next project.

But for the most part we can only speculate about these things.

Instead of the future, these stories speculate about the past.

But she would not speculate about plans for the lot.

He would not speculate about any position that might interest him.

But Sam had made up his mind not to speculate any further about the girls.

I can only speculate about the reasons for their success.

He added it was too soon to speculate about management changes.

They never speculated about other species and don't know what to make of them.

However there are a number of variables here that we can only speculate about.

How many, involving which people, I don't want to speculate about.

Hamlet's age has been much speculated about, the consensus, from various pieces of evidence, being the early 30's.

It is becoming less something to speculate about, more something to experience.

At this point, there's a lot we can only speculate about.

For reasons we can only speculate about, the Japanese left the door open the first time.

Notorious, certainly; sought after, endlessly speculated about, those too were true.

He is not speculating about when he will be ready to play in games.

Less than six hours later, we saw the beginnings of the silent fleet that so many are now speculating about.