Step 1 — Relevant industry

ENI S.p.A. is an integrated oil and gas company with major exploration and production operations, so the most relevant provided methodology is Oil And Gas Exploration And Production. The supplied methodology does not give a special alternate FFO/debt formula, so I apply the baseline S&P-style corporate calculation, while including lease liabilities in debt and using operating cash flow data to estimate FFO.

Step 2 — Estimate Adjusted EBITDA

Reported operating profit:
- Profit from operating activities = €17.510 billion

Add back non-cash operating charges:
- Depreciation and amortisation = €7.205 billion
- Impairment losses/reversals = €1.140 billion
- Write-off of tangible/intangible assets = €0.599 billion

Reconstructed EBITDA:

\[
EBITDA = 17.510 + 7.205 + 1.140 + 0.599 = 26.454
\]

Estimated Adjusted EBITDA ≈ €26.454 billion.

Step 3 — Estimate FFO

A practical S&P-style estimate of FFO can be derived from operating cash flow before working-capital movements.

Given:
- Cash flow from operating activities = €17.460 billion
- Increase/decrease in working capital = €1.279 billion

FFO estimate:

\[
FFO = CFO - working\ capital\ inflow = 17.460 - 1.279 = 16.181
\]

Estimated FFO = €16.181 billion.

Cross-check using EBITDA less cash interest and cash taxes:
- Adjusted EBITDA = €26.454 billion
- Interest paid = €0.851 billion
- Income taxes paid = €8.488 billion

\[
26.454 - 0.851 - 8.488 = 17.115
\]

This is reasonably close; I use the direct cash-flow-derived FFO of €16.181 billion because it better reflects reported operating cash generation excluding working capital.

Step 4 — Estimate Adjusted Debt

Reported financial debt at 2022 year-end:
- Short-term borrowings = €4.446 billion
- Current portion of long-term borrowings = €3.097 billion
- Long-term borrowings = €19.374 billion

Reported borrowings subtotal:

\[
4.446 + 3.097 + 19.374 = 26.917
\]

Lease liabilities:
- Current lease liabilities = €0.884 billion
- Noncurrent lease liabilities = €4.067 billion

Lease liabilities subtotal:

\[
0.884 + 4.067 = 4.951
\]

Gross debt including leases:

\[
26.917 + 4.951 = 31.868
\]

Eligible cash:
- Cash and cash equivalents = €10.155 billion

Adjusted debt:

\[
31.868 - 10.155 = 21.713
\]

Estimated Adjusted Debt = €21.713 billion.

Step 5 — Calculate FFO / Adjusted Debt

\[
FFO / Adjusted\ Debt = 16.181 / 21.713 = 0.7452
\]

<answer>0.7452</answer>