we , in the normal course of business operations , have issued product warranties related to equipment sales . also , contracts often contain standard terms and conditions which typically include a warranty and indemnification to the buyer that the goods and services purchased do not infringe on third-party intellectual property rights . the provision for estimated future costs relating to warranties is not material to the consolidated financial statements . we do not expect that any sum we may have to pay in connection with guarantees and warranties will have a material adverse effect on our consolidated financial condition , liquidity , or results of operations . unconditional purchase obligations we are obligated to make future payments under unconditional purchase obligations as summarized below: .
what is the percentage of outstanding shares among all issued shares?
approximately $ 4000 of our unconditional purchase obligations relate to helium purchases , which include crude feedstock supply to multiple helium refining plants in north america as well as refined helium purchases from sources around the world . as a rare byproduct of natural gas production in the energy sector , these helium sourcing agreements are medium- to long-term and contain take-or-pay provisions . the refined helium is distributed globally and sold as a merchant gas , primarily under medium-term requirements contracts . while contract terms in the energy sector are longer than those in merchant , helium is a rare gas used in applications with few or no substitutions because of its unique physical and chemical properties . approximately $ 330 of our long-term unconditional purchase obligations relate to feedstock supply for numerous hyco ( hydrogen , carbon monoxide , and syngas ) facilities . the price of feedstock supply is principally related to the price of natural gas . however , long-term take-or-pay sales contracts to hyco customers are generally matched to the term of the feedstock supply obligations and provide recovery of price increases in the feedstock supply . due to the matching of most long-term feedstock supply obligations to customer sales contracts , we do not believe these purchase obligations would have a material effect on our financial condition or results of operations . the unconditional purchase obligations also include other product supply and purchase commitments and electric power and natural gas supply purchase obligations , which are primarily pass-through contracts with our customers . purchase commitments to spend approximately $ 350 for additional plant and equipment are included in the unconditional purchase obligations in 2017 . in addition , we have purchase commitments totaling approximately $ 500 in 2017 and 2018 relating to our long-term sale of equipment project for saudi aramco 2019s jazan oil refinery . 18 . capital stock common stock authorized common stock consists of 300 million shares with a par value of $ 1 per share . as of 30 september 2016 , 249 million shares were issued , with 217 million outstanding . on 15 september 2011 , the board of directors authorized the repurchase of up to $ 1000 of our outstanding common stock . we repurchase shares pursuant to rules 10b5-1 and 10b-18 under the securities exchange act of 1934 , as amended , through repurchase agreements established with several brokers . we did not purchase any of our outstanding shares during fiscal year 2016 . at 30 september 2016 , $ 485.3 in share repurchase authorization remains. .