ORD Blue Line +transfer=$5 or $5.25
 

The CTA website says if you buy a single use ticket at ORD, it is $5 including transfers.
The CTA website doesn't say if you use a Ventra card and transfer from the Blue Line to a bus, is the fare $5 or $5 plus 25 cents for a transfer.

Have you used a Ventra card (not single use ticket) from O'Hare and made a transfer to a bus?

I have a Ventra card that I use once in a while when in Chicago.

The single-ride ticket at ORD comes with 2 transfers within 2 hours at no additional cost. The total cost is $5. However the transfers are good on CTA only (all of the L lines plus bus routes numbered 206 and lower).

If you are paying with a Ventra Card, $5 is deducted for the first ride when boarding at ORD. For a second ride within 2 hours on CTA, 25 cents is deducted. For a second ride on Pace (bus routes 208 and up), 30 cents is deducted. The third ride on CTA or Pace is free.

So, yes, there is a loophole in the system. If you need to transfer to a CTA vehicle, it is cheaper to buy a single-ride ticket at ORD. If you need to transfer to Pace, the single-ride ticket will not work.

Unfortunately, Ventra's crap website only allows you to go back 100 transactions of history, regardless of date. That doesn't get me back to my last ORD trip to check for sure.

That is just one loophole in the system! If you use Ventra on a bus, it is 2.25 (after April fare increase), and then you can transfer to anything (bus or L) up to 2x for 0.25 total. Ventra on the L is 2.50, and a transfer to anything is also 0.25. So if you want to ride the train and transfer only once, you'll do better (save 0.25) by finding a bus, taking it one stop, and then proceeding to your intended trip.

Yes. Absolutely right.

You can save even more by finding a Pace bus (rather than a CTA bus) and transferring to the L, since Pace fares are 25 cents less than CTA fares. (Note that Pace raised the transfer price TO a Pace bus from 25 to 30 cents for the first transfer this year, but the first transfer to a CTA bus or train from Pace is still 25 cents.)

And note that when boarding at O'Hare with a transfer, the price is still only 25 cents for the first transfer and free for the second.

You can also avoid the surcharge for boarding at O'Hare entirely by purchasing an unlimited pass.