Two Öhler system clarinets: a B♭ clarinet (left) and an A clarinet (right, with no mouthpiece).
The Öhler system (sometimes spelled "Oehler") is a system for clarinet keys developed by Oskar Öhler. Based on the Müller system clarinet, the system adds tone holes to correct intonation and acoustic deficiencies, notably of the forked notes (B♭ and F). The system has more keys than the Boehm system, up to 27 in the Voll-Öhler system (full Öhler system). It also has a narrower bore and a longer, narrower mouthpiece leading to a slightly different sound. It is used mostly in Germany and Austria. Major developments include the patent C♯, low E-F correction, fork-F/B♭ correction and fork B♭ correction. Fingering charts can be found for example in this reference.
Oskar Öhler had three students: F. Arthur Uebel, Ludwig Warschewski and K.F. Todt. Uebel and Todt are legendary clarinet makers in Germany, while Warschewski moved to Stockholm and became the solo clarinetist of Stockholm Philharmonic. Warschewski bought semi-finished Uebel clarinets and worked on the bore and mechanics. His clarinets are used by famous clarinetists like Dieter Klöcker. Uebel clarinets were used by Karl Leister when he first joined the Berlin Philharmonic; later he changed to Wurlitzer. Wurlitzer clarinets made before the 1970s sounded very much like the Uebel clarinets while the bigger bore gave them better intonation. After the 1970s, Wurlitzer made some modifications to their design. Wurlitzer clarinets are now used in the great majority of German orchestras. They are very expensive, but some Wurlitzer apprentices are producing similar clarinets for less.