* Ex-dividend adjustment takes 30 points off Nikkei - analyst
* JT, Canon, Bridgestone sold on ex-dividend trade
* Higher oil prices pressure airlines, shippers
By Ayai Tomisawa
TOKYO, June 27 (Reuters) - Japan's Nikkei share average dropped on Wednesday morning after higher oil prices hurt airlines and shippers, while companies' going ex-dividend added to the market's broader weakness.
The Nikkei fell 0.5 percent to 22,226.54 in mid-morning trade.
Companies whose business years end in December will go ex-dividend on Wednesday, after which investors will no longer qualify for the latest dividend payout.
Market participants estimated the effect of the resulting adjustment to prices would take 30 points off the Nikkei benchmark index.
Among Nikkei companies going ex-dividend on Wednesday are Japan Tobacco, Canon and Bridgestone which stumbled 4.0 percent, 3.7 percent and 2.9 percent, respectively.
Analysts said that investors remain cautious against spiralling global trade tensions between the United States and its trade partners, which has dented the market in the past week.
"We saw some short-covering on value stocks the day before, but the market is still risk averse," said Takuya Takahashi, a strategist at Daiwa Securities.
He added that while higher oil prices somewhat helped U.S. stocks overnight, more companies in the Japanese market were vulnerable to the impact of rising oil prices.
Shares in the sea transport and airline sectors underperformed and tumbled 2.4 percent and 1.4 percent, respectively, on worries about rising fuel costs.
Mitsui OSK Lines slumped 3.2 percent and Nippon Yusen declined 2.4 percent, while Japan Airlines dropped 1.3 percent and ANA Holdings shed 1.6 percent.
Oil prices rose on Wednesday following supply disruptions in Libya and Canada and after U.S. officials told oil importers to stop buying Iranian crude from November.
Chief Cabinet Secretary Yoshihide Suga told a news conference on Wednesday that Japan was closely analysing the impact of U.S. sanctions on Iran and would continue to talk with Washington and relevant nations so that Japanese firms would not be adversely affected.
Bucking the weakness, Oracle Corp Japan jumped 11 percent after the company's parent net profit rose 6.6 percent on year to 38.7 billion yen for the fiscal year ended in May.
The broader Topix declined 0.3 percent to 1,725.61. (Editing by Jacqueline Wong)