This page is showing how to install an Oracle drivers OCI
Basic Package Information
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Mon Feb 13 19:39:46 CST 2017
Client Shared Library 32-bit - 12.2.0.1.0
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#Linux
export PATH=/d/oracle/instantclient_12_2:$PATH
# Windows
set PATH=d:\oracle\instantclient_12_2;%PATH%
extension=php_oci8_12c.dll ; Use with Oracle Database 12c Instant Client
Warning: PHP Startup: Unable to load dynamic library 'D:\xampp\php\ext\php_oci8_12c.dll' - %1 is not a valid Win32 application.
Php search in the path the oci.dll and cannot load it because it's a 64 bit file. Download from the instant client page, a 32 windows instant client.