What kind of portfolio is long gamma and short vega?

short calendar spread?

Long shorter-dated options AND short longer-dated options.That's one example, I suppose.

imranyusof, i think its other way around.sell short-dated options AND buy long-dated at the money options.

I think imranyusof is right here. The short dated ATM options would have a lot of gamma, since they sit on the pin. They won't have much vega since vol is scaled by square root of time. The opposite will be true for long dated options.

yes StructCred, you are right. i have mistaken.

*chuckle*.. so was I, mate!No worries!

remember short dated vols typically much more volatile than long dated vols, so not straight forward to compare the vegas for different maturities... for example you can not have a stock crash every day forever. In the long run some type of complex "mean-reversion" in vol, personally I do not like the term mean-reversion, because hard to say what the mean is, but after big volatility shocks the volatility will over time return to more "normal" levels, this is partly reflected in long dated vols, short dated options on other hand naturally very sensitive to short term shocks...but it is more complex than this, a good topic for a book or two... it also depend on instrument etc...and there are some interesting aspects here I not have seen much written about that I soon will publish a few pieces on (in 2007)