I've been drinking G&Ts like this for years. I prefer 2 oz Gin, 3.5-4oz Tonic, .5 oz Campari and .25 oz lime juice.

Great minds think alike.

If you have a little time, try freezing the Campari (or Aperol) with the lime in a Frosun. Makes for a rather special G&T variant.

Cleaned this up a lot. It now conforms to the original recipe quoted in Beachbum Berry Remixed. Kaiser Penguin has a good comparison of the various Fogcutter recipes floating around the Internet, but basically says that the orange juice is the dangerous part of this drink and the goal is to get it into balance with everything else. Some of the many variations are noted in the Notes section.

Prefer the Colonial cocktail, which has the same ingredients, but is heavier on the grapefruit juice and lighter on the maraschino. 

I have had this a couple times and not very impressed with it. Strange enough I was looking through the Craft of the Cocktail and Dale DeGroff had a completely different version but stated it was served at the Algonquin Hotel....hmmm either way it sounded tastier then the original I've always known. 2oz light rum, 1/2oz blackberry brandy, 1/2oz Benedictine, 1/2 oz lime juice. Shaken, strained, cocktail, cherry garnish. Anyone else read anywhere to substantiate Mr DeGroffs claimed version?

Is this the best drink you're ever going to have? Definitely not. But I have to admit this is one I come back to over and over again. Maybe it's just that outside of tiki there's not all that much to do with pineapple juice before it spoils, but I think it's more than that. This drink reminds me of a style of cocktail that  doesn't seem to exist anymore. I get the same vibe with a number of different classics that combine vermouth and citrus. It just tastes so unique. Every cocktail bar has the same menu of riffs...Manhattan, Old Fashioned, Daiquiri, Negroni, etc. but no one is making stuff that tastes like this. Sure it's a little rough around the edges, but that's what makes it so good.

Updated to correct an error in a quantity ("1 1/2", not "1 1/12"), plus improve reference. This is a very delicious drink.

Looks very similar to a Rittenhouse Eye-Opener that Zorn used to serve by request at Thatch in Portland, consisting of equal parts Campari, rye (Rittenhouse, naturally), and orange juice.

1/2 lemon, 1/2 lime

The original drink was a Fizz with both lemon and lime. Over time, folk chose one or the other and dropped the soda water part. Lime is truer to form since lemon + lime still tastes more like lime than lemon.

Improved attribution, provided instructions, added detail to recipe.

Corrected spelling of 'Palo' in Notes.

To put on the wine geek hat for a second (ahem) Amontillado and Oloroso are the results of two very different styles of aging Sherry. While they're both palomino grapes, Amontillado is aged under flor and Oloroso is not, which is why Olorosos are much darker - they're not protected from oxidation by the yeast layer. Thanks,  Zachary

Correct regarding the veil. Fino/Manzanilla is even lighter than Amontillado, as it maintains the flor longer.

And Palo Cortado is accurately described as between an Amintillado and Olorosso, because, though aged under flor initially, it loses it sooner so has been aged oxidatively for some time between the two.