The British Oliver Manufacturing Company branded many European models with the Oliver name.
The first portable typewriter to bear the Oliver name is the Fortuna.
The fourth Oliver portable is a rebranded Swiss machine called the Patria. It was produced from 1948 to 1954.
With nearly half a million machines produced, the Oliver No. 9 is by far the most common Oliver model. This model introduced shift keys on both sides of the keyboard.
Some Oliver No. 9 machines have the keys staggered differently. Traditionally, looking from left to right, the keys protrude from the top row, the bottow row, and then the middle row. The alternate keyboard staggers in order, from the top row, the middle row, and then the bottom row. Some of the symbols and other characters were also rearranged on the alternate keyboard.
The machines with these alternate keyboards have an "A" prefix on the serial number. example I know of is my machine, serial number A900380X. After this machine, the only other example I could find before serial number A980001 is A928771X. Beginning with A980001, all model 9 machines were given the "A" prefix and alternate keyboard. Note that this excludes Oliver No. L-10 machines which have a Spanish keyboard with the traditional staggered layout and therefore do not have an "A" prefix.
The only two machines I know to exist with an "X" suffix are the ones listed above. My machine, A900380X, has flat-cut side handles with two screws in each handle. Side handles are made like this if a bracket to support a wide carriage is installed. However, there are no brackets nor a wide carriage on this machine. Perhaps this is related to the "X" suffix.
The Oliver No. 11 was the last Oliver model produced for the domestic market. Compared to its predecessors, the Oliver No. 11 was given a different look. The iconic olive green paint was discontinued in favor of gloss black accented with gold pinstriping. The Oliver logo was redesigned using a thin lettering.The side handles were replaced with side cutouts to lift the machine. Many sources say that only 35,000 model 11s were produced. However, this is incorrect; 50,000 Oliver 11s were produced. I have seen Oliver No. 11 serial number 1049945 to help back this claim.
Some model 11 (also 12, L-12, and L-13) serial numbers have a "B" prefix. Unlike the "A" prefix on Oliver No. 9 machines which denotes an alternate keyboard, the "B" prefix has no correlation to the keyboard. Some machines with a "B" prefix have the alternate keyboard and some do not. I have yet to figure out what the "B" prefix means.