I know there is a way to discover collusion with Sharkscope.
On PKR i usually find at the tables 2 players.
- they're from the same city in Brasil (and it's not Rio or San Paolo, but a small city with less than 300,000 inhabitants)
- i've ALWAYS seen them together at the table, i don't remember a single time i've seen just one of them
- they NEVER fight for a pot
Also other players have suspects against them.
I know there is a way to compare their ROI when they play together and when they don't (i think it never happens...)
Can someone please explain me how to do that?
Thank you Pharr... but i've just discovered that is a subscriber functionality 
Whatever... i'll report it to PKR, and they'll know how to check it, i think.
I know at Poker Stars they do a great job of investigating claims of cheating. I have caught players soft seating each other at the end of tourneys and reported it. They did a thourogh investigation and refunded the winnings and buy in. They also tell you the punishment of the players. They have the ability look at hole cards and can see if certain plays make sense. We were down to 3 players in an mtt about a year ago and this idiot folded ak to his buddy when he was in the small blind and his buddy had like 400 chips remaining. It was obvious to me because any hand wuda been worth a shove with the player being so short stacked. Not only that they both were talking sht to me. I was guilty too of talking, but only after it became obvious that these two were cheating. For me its not usually an issue tho because 90% of the time i play heads up. But the one time it was i found PS to be very professional about the situation.
I have had a very similar situation of two players that i noticed were always at the same sit n go table as each other. I was a little bit suspicious so emailed Pokerstars about it and a couple of weeks later got a response saying they had been investiagted and found to be in breach of the rules. Pokrstars also said they were no longer welcome to play at the site.
I agree with goodfella that Pokerstars are excellent at dealing with this type of issue, and with regards to the situation at PKR id just do the same. Report your suspicions and im sure they'll investigate everything and get back to you with their findngs.
Akaka is one of them called Mont........, I did report two guys who played exclusively against each other in july 2009, and were clearly colluding or the same person. I think they were banned, but funnily enough neither account was showing profit on SS lol.
I'd be very disappointed if these cheats were back!
It's so long ago I am struggling to recall the user names or the place, was Brazil I think, maybe somewhere beginning with P?
@ AKAKA: Just stop playing DoNs, many players collude, its insane. Just play regular SNG or MTT, much better.
@Jenny: no, sis. Their names are DoyleT****** and jorge2****
@Viper & Goodfella: thank you, i'll report it to PKR for sure.
Let me know what happens, im sure you will be impressed by the way it gets handled.
We'll se, mate. Thank you 
I'll keep you updated.
Come on AKAKA have they been banned then?????
search one player, the go to the options thing for head to head and type in the other player.
it will show their roi together and apart and how many games played together/apart.
that is very useful