What is the size of online gambling industry? Size in terms of 
a) revenue
b) users
c) operators

I am looking for market research data regarding
a) what kind of growth this industry has seen in last 5 years.
b) what kind of future analysts predict for this industry

Data from any other "credible" and "quotable" source will do.

By online gambling, i mean: online casinos + online poker + online sports betting.

<Online gambling.

Online gambling has grown from 30 sites and bets of $17 million in
1996 to approximately $3 billion in wagers in 2000. US gamblers bet an
estimated $6 billion in 2003.
Source: AngelCiti Entertainment.
http://www.angelciti.com/aboutus.asp

In 2000 gambling sites had revenue of approximately $2.2 billion
(Christian Capitol Advisors) at that time there were about 1400 online
casinos.
http://www.the-surfs-up.com/news/gamblingonlinenews.html

2001
The gaming board for Great Britain gives an estimate for the total
amount of global online gambling and a breakdown of the amounts spent
on each type of gambling.
Total global gambling turnover (offline and online) - £638 billion.
Total online gambling ? £21 billion
Online Horseracing - £2 billion
Online Sports betting - £9 billion
Online casinos - £5 billion
Online Lotteries - £5 billion
http://www.gbgb.org.uk/intgambling.htm

Gross online sports wagering for 2003 will reach $63.5 billion.
Source: Christiansen Capital Advisors, LLC.
http://www.usatoday.com/money/covers/2002-03-29-online-bets.htm

This CNN article has a graph showing online wagers from 2001 and
projected online wagers worldwide up to 2010 - $18.4 billion (source:
Christiansen Capital Advisors). Although the figures are supposedly
the amount wagered, they appear to be gross revenue (bets less
winnings).
http://money.cnn.com/2004/03/26/commentary/column_sportsbiz/sportsbiz/

According to Merrill Lynch, gross gaming revenues for online betting
will reach $48 billion by 2010.
http://www.gamblingmagazine.com/articles/starnet/starnet152.htm

According to the Online Gambling Research and Markets Group, online
gambling will reach $125 billion by 2015.
http://www.gamblingmagazine.com/ManageArticle.asp?C=500&A=10546

Merrill Lynch predict that online gambling will grow to $177 billion
by 2015. $100 billion will come from online sports betting.
http://66.102.11.104/search?q=cache:ig472u3x-JwJ:www.dentonwildesapte.com/assets/O/OnlineGambling_Oct2001.pdf+%22sports+betting%22+billion+%22by+2015%22&hl=en

Number of gamblers.
There are approximately 12 million online gamblers. 5.3 million are
Americans. 4 million are from Asia. By 2006 the number of Asian
gamblers is anticipated to grow to 7.4 million.
Source: Christiansen Capital advisors.
http://www.casinomeister.com/news/april2003.html

Number of operators.
The number of online gambling sites in 2001 was 31,000. Source: Websense.
http://www.websense.com/company/news/pr/Display.php?Release=010620360

The number of online gambling sites in 2002 was 32,991 and 44,076 in
2003. Source: Websense.
http://www.shoutasia.com/websense/clients_websense_gamble.htm

In 2004 there were an estimated 53,000 online gambling sites.
Source: As the Athens 2004 Summer Olympics Get Underway, So Does
Reduced Productivity, Increased Legal Liability and Bandwidth Usage.
PR News.
http://www.prnewswire.com/cgi-bin/stories.pl?ACCT=104&STORY=/www/story/08-12-2004/0002230373&EDATE=>


<Search strategy:>

<"online gambling" growth>
<://www.google.com/search?hl=en&lr=&ie=UTF-8&q=%22online+gambling%22+growth>

<"online gambling" billion>
<://www.google.com/search?hl=en&lr=&ie=UTF-8&q=%22online+gambling%22+billion>

<websense "online gambling sites">
<://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&rls=GGLD%2CGGLD%3A2005-17%2CGGLD%3Aen&q=websense+%22online+gambling+sites%22>


<Hope this helps.>

Hey, don't know if this will be helpful for you, but i have recently
been hired in an online casino(and sports book). 300 000+ active
members. Though i don't know the actual revenue, I was told an analogy
a few weeks ago; "if for the super bowl last year, (with over $7
million in wagers the day of) every wager that was placed, was on the
underdogs, and the underdogs won, the current interest on the money in
the bank would more then cover ALL the payouts."

That kinda blew my mind when I was told... but hope that is in some way helpful.

considering its global there is still a long way to go.
it all depends on regulations and how individual governements react in
order to either clamp down on it or tax it.
i am in the uk and i play at www.clubworldcasinos.com they are
regulated offshore but in my experience are very fair.