These two regions represent most wines that you’ll find from the southern half of Portugal. Lisboa is made up of a number of interesting sub-regions (detailed below), and Alentejo is one large area that is made of a mix of larger and smaller producers, making low cost to high cost wine. In other words, massive variety.
One thing to point out at this point is what a ‘big’ winery means in Portugal.
A big winery in Portugal is still small. This is very important to keep in mind. It’s still family owned and operated. It still works with a wide range of farmers. It still has local pride and individuality. There is no such thing as a Franzia, Gallo, or Constellation (a huge group that owns a ton of wineries in California and elsewhere) in Portugal. The largest wine company in Portugal is Sogrape, which is larger than the next seven on the list combined. Their total sales amount to $250 million, compared to Gallo in California at $3.6 billion.
Lisboa
Map resource (and article), Wine Enthusiast: Lisboa, Land of Fresh Wines
Vineyards.com: Map of Lisboa Wine Regions
Wines of Portugal: About Lisboa Wines
Wikipedia: Lisboa Wine Region (with links to the articles on the sub-regions within)
Decanter: Lisboa Travel Guide for Wine Lovers
Winesearcher: Obidos
NY Times (possible paywall): Colares, Where the Vines Snake Through the Sand
Chambers St. Wines: Back to the Beach: Wines of Colares (great photos!)
Wine Anorak: Tasting old Colares
Alentejo
SevenFifty Daily: Alentejo (this was a sponsored post on SevenFifty, but is totally comprehensive and a bit of a masterclass on the region, including maps)
Cycling Centuries: Everything You Want to Know About Cork Oak Trees
The Treeographer: The Whistler Tree (the oldest cork oak in Portugal … super neat article)