Hotels.com uses a quasi-revenue based loyalty programme. Rather than awarding points per unit of currency spent, it gives you a voucher for a free night when you spend 10 nights. The value of the free night voucher is the mean average of all the 10 nights.
A coupon just dropped into my inbox for their latest promotion – a pretty generous one at that too. You should see if you have received the same one.
For one booking made before 27th March 2017 on the UK version of Hotels.com for a stay until 13th July 2017, you will receive double the reward nights which will count towards your free nights voucher. So rather than 10 nights to collect one free night, you can claim it in just 5 nights, essentially halving the effort or doubling the loyalty reward for that stay depending how you look at it.
The promotion is limited to the first 65 000 coupons, and you must pick a rate which is pre-paid and not paid at the hotel. If you cancel your booking you will lose the coupon.
Though you must book on the UK version of the site, the T&C does not that the hotel must be located in any particular region. I would be very surprised if that's the case and I would safely assume it is for all properties worldwide, subject to the pre-paid rate stated above.