BP will this week reveal that it has cleared itself of gross negligence after an internal inquiry into the causes of the Deepwater Horizon explosion.

The company believes evidence will emerge of the role that other oil companies and contractors on the project had in causing the worst environmental disaster in US history. But this is unlikely to satisfy its critics. During congressional hearings in the US, politicians have laid the blame for the disaster squarely on BP, accusing it of ignoring standard oil industry safety practices to save money.

Pressure is also mounting on the company to clarify the position of chief executive Tony Hayward at its half-year results meeting on Tuesday. There is growing speculation that, alongside the figures, BP could announce Hayward's departure, although he could stay on until a relief well is in place in the gulf. A board meeting is scheduled for tomorrow, but a BP spokesman refused to comment on whether the succession issue was on the agenda or whether there would be an announcement about Hayward at Tuesday's results.

The company will publish the full findings of the inquiry into the causes of the gulf oil spill when it is completed next month. BP accepts that it will have to shoulder some blame for the accident. But it is understood that the company has found no evidence of gross negligence and does not expect any to come to light in the future. It will robustly defend itself against such claims.

If investigators rule that BP is guilty of gross negligence, the firm would face a far heftier bill: under the US's Clean Water Act, BP currently faces fines of $1,100 (£715) for each barrel of oil spilt, but a such a ruling could see the figure rise to $4,300. If BP were the sole party to be found grossly negligent, it would also be liable for the entire clean-up and compensation bill. BP owns 65% of the Macondo well on which the Deepwater Horizon was operating, with 25% held by Texas-based Anadarko and the remainder by the Japanese company Mitsui.

Anadarko has so far refused to pay any costs, while Mitsui has not made its position clear. BP will continue to pay for the clean-up – which now totals $4bn – and bill its partners for their share.

A US oil lawyer said most indemnity agreements and insurance would protect BP against claims even it was found guilty of ordinary negligence, but would be void in a case of gross negligence. Such a finding would have "far-reaching consequences" for BP and its partners' and contractors' liabilities, he said.

BP will also give the City guidance on the likely costs from the disaster this week. Analysts at Barclays Capital believe the provisions could exceed $25bn. Stripping out the costs relating to the disaster, BNP Paribas forecasts BP's net income for the second quarter at just under $5bn, up by 68% compared with the previous year – the biggest rise of all its European oil industry peers.

Hayward will also indicate which assets are core, and which peripheral, for the company in the future. BP is looking to sell more assets to shore up its balance sheet. It will continue to focus on its three core areas: deepwater oil and gas, "unconventional gas" (for example, from shale or coalbeds) and using new technologies to squeeze more oil and gas from major mature fields.

Next month BP is expected to finish handing over responsibility for compensation claims to Kenneth Feinberg, who has been appointed by the White House to administer a $20bn fund paid for by the company. BP does not expect to have to pay out the full $20bn. Damages arising from other legal action, and from the completion of formal investigations into the accident, are likely to be more costly.