There are a couple of things to look at but I would suspect that either
you have the strap too tight causing a small fold or deformation of the
skirt, or the mask holds too much air and lifts up against the nose to a
spot where it doesn't seal like in the shop.

My daughter had a mask that sealed perfectly in the shop, but when she
cinched up the strap, it folded ever so slightly causing a steady drip.

I had a large Scubapro mask that fit beautifully in the shop but was a
high volume and the large bubble constantly lifted up on the mask
jamming into the base of my nose.  Besides hurting after a half hour or
so, it seeped.  I have since gone back to low volume.

Just my $.02

"canes88" <u18257@uwe> pounded away at his keyboard resulting in:

Tight seals?  Maybe you should loosen the strap.  Seems
counter-intuitive, but it might work.

Dan Bracuk
If we don't succeed, we run the risk of failure.

Purge valve has it's merits, but personally I don't like it since I
occationally need to grab my nose to equalize and the valves I've seen
make it a bit harder, especially with the gloves I'm using.

I would't mind clearing the mask once in 15 minutes, I probably do it
nowadays quite a bit more often. I use word "probably" because it is so
automatic that I don't register it at all.

Not knowing the details, here are some suggestions:
1. Buy your masks in person.  You can't try a mask that you buy on line
before you pay for it.  If you find a make and model that fits you properly,
then buy on line.
2. Guy your masks in a shop where the salesman knows something about diving.
The problem you are having is easiest to fix with expert help.
3. Buy a spare mouthpiece for your regulator and take it with you when you
shop for a mask.  You should have one anyway.  Your face with a mouthpiece
in it is not the same shape as your face without one.
4. If you're not easy to fit, heck, even if you are easy to fit, one of the
expanded view masks may not be for you.  I have two of them that fit in the
ship that won't work in the water.  They're just too damned particular about
any change in the shape of the fact their on.

Others have suggested you try loosening the strap.  If you have your mask
too tight, this may be the source of your problem.  Of course, too loose is
a problem too.  Start a bit loose and tighten it up a bit until you get the
best results.  If this doesn't work, look for a new mask.

Good luck.

Lee

No, it's not too much to expect.  It's unusual to have a mask leak in normal
diving.

A purge valve only allows you to clear your mask without breaking the seal.
It's a remote possibility that clearing your mask is what is causes the
leaking.

You've gotten some good suggestions with mask strap tension and fitting the
mask with mouthpiece in place.  Try those to see if they work.

You could try having someone who knows what they are doing with you to fit
the mask and then check it underwater.  It would be helpful to know where
the mask leaks, if it leaks in the same place consistently, and if it looks
like it's properly fit at depth.  To have three different masks with the
same problem seems odd.  Fitting a mask is not as easy as it appears but it
is not that difficult either.  There are many good tips in previous threads
on how to fit a mask properly.  Improper fit is the biggest cause of the
symptoms you describe but that's not the only cause.  I've had two masks
leak around the lenses - one because I dropped it and the other leaked new
out of the box from the factory.

You'll enjoy diving much more without the leaking mask.

My wife had a persistant leak that no adjustment to the strap or shifting
position on face would fix. Mask was only one season old and hadn't leaked
last year. Prescription bifocal lenses so replacement was not high on the
list of fixes. LDS came up with an idea I'd have never thought of.....change
reg mouthpiece. Put on a smaller mouthpiece and leak was instantly gone. No
further problems. Worth a try??? I have also heard of -very rare- leaks
between the lens and frame. This might only occur at depth and not be
noticable at the surface. If this is the case nothing you do will make any
difference and it is a warranty issue.

Gary

all the other answers are good - here's one more. Stop exhaling through
your nose ( except for mask squeeze ). Air out = water in.

I've had a simular problem and have gone thru 3 different masks to try and
fix it. What I found was that if I have the mask positioned higher up on my
face it tends to leak. If I postion it so the bottom of the mask is closer
to my upper lip, I get no leaks.  Give it a try.

Dave

Zillions of good suggestions here... do U use sunscreen?  I found it always
used to cause a slow leak on my mask a few years back--don't use it anymore.
You also might have one of those faces that won't work with the mask U have.
Not too tight, not too loose is good advice.
Had a buddy who ALWAYS put silicone grease above his lip to keep it from
leaking--kinda negates the sunscreen theory, but whatever works... I've seen
other guys use Vaseline--not a good idea on rubber, but might not be as bad
on silicone...?