(Updates to close) Dec 12 (Reuters) - Australian shares ended...

(Updates to close)

Dec 12 (Reuters) - Australian shares ended Monday flat with an upside bias, after hitting their highest in four months in early trading, underpinned by oil and gas stocks.

The energy index .AXEJ jumped to its highest since Oct. 12, 2015, after oil prices rose to the highest in a year and a half high on Monday, after OPEC and non-OPEC producers agreed to cut oil output. [O/R]

Majors Oil Search (OSH) and Woodside Energy (WPL) both rose more than 3 percent.

The S&P/ASX 200 index (xjo) ended 2.2 points or 0.04 percent higher at 5560.6, its highest close since Aug 1, after surrendering some early session gains as investors turned their attention to an interest rate hike expected from the Federal Open Market Committee meeting this week.

Financials added gains, with three of the "Big Four" banks up. ANZ Bank (ANZ) ended 0.3 percent lower.

Exchange operator ASX Ltd (ASX) shed 0.2 percent, while Seven West Media (SWM) rose 0.7 percent to its highest in two months.

Large cap grocer Woolworths (WOW) slipped 0.3 percent. Its rival, Wesfarmers Ltd (WES), ended in positive territory.

New Zealand's benchmark S&P/NZX 50 index (nz50) slipped 0.25 percent or 17.26 points, to finish the session at 6876.04, hurt by consumer staples.

A2 Milk (ATM) was the biggest loser on the index, ending the session down 5 percent.

But Fonterra Co-Op (FCG), the world's biggest dairy exporter, however, gained 0.17 percent after it confirmed a forecast farmgate price of NZ$6 per kilogram.