How to earn by running a shorten url website?

I noticed that even Google offers shorten url service.

I am not sure how to make money if I run a shorten url service like google, bit.ly, tinyurl?

There are so many shorten url php script so it's not difficult to make a shorten url site.

I have think and search some articles over internet.
There seems no obvious making money way on shorten url website.

Is there anyone here make money from building a shorten url service?

 

some of these sites sell you extra reporting, faster redirect, etc

 

I use gool.gl (Google URL Shortener) for few times.
Google offers reporting and redirect pretty faster for free.

I see no ads on gool.gl now. It might be another free service by Google

 

I run a short url service and have thought about showing ads before redirecting to the site but that could possibly drive away users.

 

One friend come to visit me and told me that he builds a short url service with a xxx.tc numberic domain.
It seems that a short domain also important to a short url website.

It's also hard to find a cheap and short domain.
Besides, I am not sure how to easy to deal with the spam or trash redirect links.

 

This is also something I have been thinking about lately. The only simple ways I can think of are as tinyURL do and that is i) have ads on the shorten page - if the service becomes popular, then the page will get a lot of traffic. Doesn't have to be PPC ads...maybe banner ads to your own money sites And ii) to have a donate button on the site.