# Relationship history for MSHA mine 1601321

Current hierarchy: **National Oilwell Varco Inc → National Oilwell Varco LP → National Oilwell Varco LP**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-17T05:35:58.500035+00:00

## Valid-time edges

- **operator_operates_mine:** Ambar Inc → National Oilwell Varco LP; 1997-10-01 to 2000-10-01; source msha-controller-operator-history
- **controller_controls_mine:** Beacon Group Energy Investment Fund Lp → National Oilwell Varco LP; 1997-10-01 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Beacon Group Energy Investment Fund Lp → Ambar Inc; 1997-10-01 to 2000-10-01; source msha-controller-operator-history
- **operator_operates_mine:** Ambar Lonestar Fluid Services LP LLLP → National Oilwell Varco LP; 2000-10-02 to 2010-03-14; source msha-controller-operator-history
- **controller_controls_mine:** PATTERSON ENERGY INC → National Oilwell Varco LP; 2000-10-02 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** PATTERSON ENERGY INC → Ambar Lonestar Fluid Services LP LLLP; 2000-10-02 to 2010-03-14; source msha-controller-operator-history
- **controller_controls_mine:** National Oilwell Varco Inc → National Oilwell Varco LP; 2009-07-13 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** National Oilwell Varco LP → National Oilwell Varco LP; 2010-03-15 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** National Oilwell Varco Inc → National Oilwell Varco LP; 2010-03-15 to current/open; source msha-controller-operator-history