Extract contents of zip files to a common folder /Library/Oracle/instantclient_11_2
The next step is to copy the necessary files into your OS X dynamic library and bin directories. Open a terminal window and go to the directory above the one you created containing all the files you unzipped.
Download the source for the version of php that you are using in MAMP (e.g.: 5.4.42 in this case).
Extract the PHP source file and move the created folder to the following location (based on PHP version): /Applications/MAMP/bin/php/php5.3.29/include/php. (The contents of the extracted folder should be in the root of ../include/php)
navigate to include/php folder and execute ./configure
Run sudo pecl install oci8
When Prompted, use instantclient,/Library/Oracle/instantclient_11_2/ as the Oracle instant Client path.
If you faced an error for AUTOCONF not found, (you don't have it installed in your MAC)