The deal for an additional 60 Boeing jets brings the total number of 737s ordered by Air Berlin to 85, and comes a week after Boeing received a $5.5 billion order for 25 passenger and freighter aircraft from Korean Air Co.
The recent run of orders extends Boeing's lead over European rival Airbus, which has been struggling with an array of design and production problems on its commercial jets.
Boeing is staging a comeback after being beaten by Airbus, which is majority owned by EADS, in annual plane orders for the past five years.
The latest deal with Air Berlin, the second-largest airline in Germany, makes it the largest order of 737s from Germany.
In August, Air Berlin ordered 25 Boeing planes.
The 737-800 Next Generation aircraft are to be delivered between 2007 and 2014.
Air Berlin's subsidiary DBA is to receive 25 of the planes.