Apple is reportedly working on a 15-inch MacBook model and is in the test phase, according to the Japanese-language site Macotakara.

It is unclear whether the new notebook would be called MacBook Air or new Macbook Pro, but the report says it would be an extension to the MacBook Air lineup.

The report also said Apple is developing a next generation MacBook Pro, which would not have built-in optical-disk drive.

Recently, Apple upgraded its entire MacBook Pro lineup with faster processors and better internal storage without changing prices, to capitalize on the holiday buying season.

The entry-level 13-inch MacBookPro comes in two versions, a $1,199 version that comes with a 2.4 Intel Core i5 processor, 500 GB of storage space and 4Gb of RAM. The early 2011 versions that are being sold in stores right now only have a 2.3GHz dual-core Intel Core i5 chip, 4GB of RAM and 320 GB of hard drive.

The faster 13-inch MacBook Pro will still sell for $1,499 but will come with a newer 2.8GHz dual core i7 processor up from the early 2011 version with 2.7 GHz processor. It will also have a bigger hard drive capacity of 750GB up from its previous 500GB version.

MacBooks are a significant contributor to Apple's revenues apart from iPhones and iPads. For its fourth quarter which ended on Sept. 24, the company sold 4.89 million Macs, a 26 percent unit increase over the year-ago quarter.